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- Nat Nanotechnol 6(11):683-688 (2011)
Nature Nanotechnology | Commentary The communication challenges presented by nanofoods * Timothy V. Duncan1Journal name:Nature NanotechnologyVolume: 6,Pages:683–688Year published:(2011)DOI:doi:10.1038/nnano.2011.193Published online30 October 2011 Nanotechnology has the potential to lead to healthier, safer and better tasting foods, and improved food packaging, but the hesitation of the food industry and public fears in some countries about tampering with nature may be holding back the introduction of nanofoods. Subject terms: * Environmental, health and safety issues * Ethical, legal and other societal issues * Industry and IPR Article tools * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Nanotechnology is unusual in that it has been hijacked as a brand name to market various products that have nothing to do with the nanoscale, such as portable music players (iPod Nano), cars (Tata Nano) and computer devices (Logitech nano cordless mouse), whereas products that do contain nanomaterials often avoid reference to the term 'nano'. In most countries, there is still uncertainty surrounding how the government bodies responsible for consumer product safety will regulate nanomaterials, and this might explain the reluctance of some companies to use the term nano in their marketing. It is also possible that companies fear that they might be targeted by consumer advocacy groups. However, this reluctance might also reflect general uncertainty over how the public currently views nanoscience or is likely to view it in the future. The lingering possibility that consumers might reject nanotechnology products out of concern about the impact of nanomaterials on human health and! the environment is, therefore, likely to be one of the reasons why the commercialization of nanotechnology is not keeping pace with basic research in nanoscience1. To combat this uncertainty, dozens of studies have been performed in an effort to understand how members of the public currently view nanoscience, and to elucidate the factors that influence those perceptions, so that public attitudes towards nanotechnology might be improved. The most notable finding of this collective body of research is that public awareness of nanotechnology remains low2, 3, 4, 5, 6, 7, 8. A survey in 2009 found that 70% of Americans had heard little or nothing about nanotechnology4, a situation that has not changed appreciably over the past few years4, 6, 8. Even so, public opinion ranges from neutral to cautiously optimistic, with perceived benefits typically outweighing perceived risks2, 6, 7, 9, 10, 11, 12. Factors found to influence perceptions of nanotechnology are myriad; they include cultural worldview, religiosity, governance philosophy, knowledge and familiarity level, trust (in government, scientists or industry), emotion, age, gender, race/eth! nicity, education, general knowledge of/attitude towards science and awareness of previous technology-based controversies. A meta-analysis of studies that probed these and additional variables found to influence risk judgements of nanotechnology has recently been published6. Consumer attitudes towards nanotechnology will continue to evolve, and one agent that will drive this change is the mass media. Laypeople acquire their information about scientific topics primarily from television, newspapers, magazines and online news sites, and one way in which these sources can affect public attitudes towards new and existing technologies is the amplification of consumer risk perceptions through the disproportionate amount of attention that the media pay to controversy13. It is, for example, well accepted that the mass media is partly responsible for the erosion of public trust in government regulatory agencies in the UK following a chain of well-publicized food crises in recent decades13, 14, and this has also reduced the willingness of consumers in the rest of Europe to accept foods made from genetically modified organisms (GMOs). Many in the nanotechnology community worried that this negative media attention would also create an environment of distrust! that could foster public opposition to nanotechnology, and indeed, some research has already found that European citizens are generally less willing to embrace nanotechnology than US citizens15. Correspondingly, several studies have provided evidence that media coverage of nanotechnology has tended to be more negative in Europe than the United States15, 16, 17. Consumers' attitudes towards science and new technologies are strongly influenced by how much trust they have in the individuals and organizations responsible for protecting public interests. A media-catalysed crisis of confidence surrounding a single nanotechnology application or product could easily initiate a chain reaction of events that not only compromises the future marketability of unrelated nanotechnology-based products, but also places a significant burden on the ability of government agencies to regulate them. The future of nanotechnology is thus only as secure as the public's willingness to accept those applications that are especially vulnerable to dread, fear and other negative emotions, and these applications certainly include nanofoods18, 19. Therefore, early identification of the key issues that influence the acceptability of nanofoods, followed by actions to address these issues, are required as part of a proactive strategy to ensure the long-term success o! f beneficial applications across all of nanotechnology. Fearing the unnatural * Fearing the unnatural * What governments are doing * What industry can do * Media matters * Outlook * References * Acknowledgements * Author information Among the types of products that may benefit from nanoscience, foods are unusual in the potency of the emotional connection consumers have with them. Food chemist Peter Belton wrote20 that "acceptability of food is often a matter of how we identify ourselves and our position in society rather than whether the food is physiologically valuable or harmful". Food is extensively integrated into human courtship and marriage ceremonies21, 22, and is also deeply connected to cultural beliefs, religious rituals, and racial, ethnic, and gender identity23, 24, 25. Attitudes towards new food technologies, therefore, are often not formed by objective assessments of their sensory characteristics, nutritive value or safety, and they are extremely susceptible to damage by negative emotions and bad publicity20, 26, 27. Nanotechnology offers many potential benefits to the food industry (Fig. 1)28. Nanocomposite plastics could provide the basis for strong packages with high barriers to oxygen and water vapour; silver and metal oxide nanoparticles are potent antimicrobial agents that can kill foodborne pathogens; nanosensors offer new ways to detect gases, microbes or chemical contaminants in complex food matrices; and nanoencapsulation may help fortify staple foods with essential nutrients. Despite these potential benefits, however, some studies have suggested that consumers are wary about nanofoods. For instance, food applications of nanotechnology have one of lowest public acceptance levels in Australia out of all the applications asked about7, and only 7% of Americans would purchase nanofoods without more information on the associated risks of doing so29. Figure 1: Nanotechnology offers potential benefits to many areas of the food industry including (clockwise from top left) agriculture, food processing, food packaging and the nutritional aspects of food. Of these areas, applications of nanotechnology in food packaging are nearest to the market. Reproduced with permission from ref. 28, © 2011 Elsevier Inc. * Full size image (88 KB) Research has indicated that some of this wariness may derive from dread of the possible adverse health effects of food and health applications of nanotechnology3. Furthermore, focus groups have revealed worries that the wealthy will benefit disproportionately from new health applications of nanotechnology30, suggesting that this may be an additional public concern surrounding nanofoods. Admittedly, most studies from which these conclusions are drawn were based on small population sizes or were not otherwise designed to broadly probe public perceptions of nanofoods, and so more opinion research on this topic is sorely needed. Available data suggest that one of the reasons some people may be hesitant to purchase nanofoods is that the physiological benefits of consumption often cannot be easily experienced31. Instead, consumers must rely on industry leaders and scientists to convey what the benefits of new food technologies are, and the efficiency of this communication is highly dependent on trust in these individuals27. Moreover, Siegrist and co-workers have found that trust in the food industry, research scientists and government agencies impacts the perceived benefits of nanotechnology applications in the food sector much more than it influences the perceived risks32, and our willingness to buy a food product containing a nanomaterial depends more on how beneficial the product is believed to be than on what the perceived risks are31. Nevertheless, perceived risks are still a concern because many people have an 'all or none' view of toxicity when it comes to rationalizing potentially hazardous ch! emicals against dosage and exposure33. This is especially relevant for nanofoods, in which the allegedly risky substance will be directly consumed. The fact that many consumers do not appear to take account of dosage when assessing the risks associated with nanofoods suggests that other important information about food safety might also get 'lost in translation' in exchanges between scientists and consumers. However, improved communication of risks and benefits alone will not ensure acceptance of nanofoods, because perceptions of naturalness also play an influential role. Social scientists are still actively researching what constitutes a 'natural' product in the minds of consumers34, yet it is clear that associations with naturalness are almost entirely positive. Moreover, although a connection between naturalness and physical benefits to health and the environment has been demonstrated, a substantial portion of preference for natural foods is ideational — that is, it is based on morals, aesthetics or other cultural/religious factors that are not related to empirical benefits such as nutrition or safety35. Naturalness is also grounded primarily in the type of process by which a product is made rather than in its actual content36, 37, at least for ethically contentious manipulations34. For instance, although selective breeding of animals or plants can take years of human intervention and results in genomes that are vastly different from ancestral starting materials, such organisms are rated as far more natural than genetically modified organisms possessing single allele replacements36. This counterintuitive result has been attributed to human fears of the consequences of 'tampering with nature' and a perception that manipulation of life at the molecular level is more obtrusive and less morally acceptable than the same process applied from the top-down and over longer periods of time27, 38. Note that dread from these sources is probably augmented when the perceived unnatural substance is intended to be actively ingested, as it is in the case of a novel food item. Naturalness heavily influences the types of nanotechnology products likely to be accepted by consumers, and not surprisingly this is particularly relevant for food-related nanoscience applications33. Some evidence suggests that individuals who prefer 'natural' products may be more likely to believe that food-related nanotechnology applications are risky and offer few benefits32. Furthermore, an aversion to nanotechnology products perceived as being unnatural can override even clearly communicated benefit information, as illustrated by a willingness of consumers to forego a health benefit (for example, cancer prevention) associated with eating a dairy product containing nanoparticles, if this product was perceived to be less natural than a nanoparticle-free version39. Naturalness may also explain why food-packaging applications seem to enjoy greater support than nanomaterials added directly to food7, 31, 32, given public aversion to molecular-level manipulation of food and th! e fact that food packages are often composed of materials that are not natural even in the absence of nanomaterials. Experts and laypeople assess nanotechnology risks differently3. Thus, some scientists may become frustrated when the public's worries about naturalness or other social issues divert attention away from scientifically grounded efforts to probe the risks that nanofoods pose to human health and the environment. Nevertheless, public acceptability will ultimately depend on what the public perceives the risks of nanofoods to be, irrespective of what scientists determine, and so stakeholders ignore ethical and social concerns at their peril. The future of nanofoods is therefore critically dependent on food companies and governments being able to use the outputs of scientific risk analyses to guide technological development and commercialization while simultaneously being sensitive to the different kinds of risks that the public is concerned about. Fundamentally, this becomes an issue of communication, one which will be particularly challenging because there are social and cultural factors associated with food that are not usually found in traditional risk-communication frameworks. What governments are doing * Fearing the unnatural * What governments are doing * What industry can do * Media matters * Outlook * References * Acknowledgements * Author information © ISTOCKPHOTO.COM/XYNO Nanotechnology could lead to better foods and food packaging, but the food industry has been criticized for being reluctant to talk about nanotechnology. In an effort to prevent the same kind of communication failures that seriously impeded the adoption of agricultural biotechnology within the food industry, many stakeholders in nanotechnology have been proactive at engaging the public at an early stage of commercial development40, 41. For instance, the 6th and 7th Framework Programmes in the European Union, and the National Nanotechnology Initiative in the United States, both fund projects to study the social and ethical implications of nanotechnology, and to initiate public engagement exercises. Moreover, the manner in which interested parties are approaching public engagement about nanotechnology is also changing42. New risk-management paradigms that seek to include bidirectional communication between the public and other technology stakeholders at multiple stages of the risk analysis and policy evaluation process are becoming increasingly popular43. The incorporation of 'concern assessments' alongside traditional health and environmental risk assessments is now considered an effective means to ensure that decision-makers account for how the public filters technological risk information through their values, morals and emotions44. Indeed, numerous researchers in risk research have advocated a tailored or targeted approach to risk management that specifically takes into account the specific risk perceptions, values or cultures of different groups to improve the way in which information about risks and other health-related matters is communicated42, 45, 46, 47, 48. G! iven that the public acceptance of nanofoods will be heavily dependent on factors that are not related to perceived toxicological or environmental risks, these new approaches to thinking about risk are likely to become more useful as the public debate over nanotechnology unfolds. Although nanotechnology-related public engagement and trust-building exercises have so far been cautiously viewed as successes, there continues to be numerous challenges to communicating effectively with the public about nanoscience49, 50. One of the biggest challenges is the fact that nanotechnology encompasses numerous different areas of science and technology, so public dialogues by necessity offer only superficial treatments of issues that citizens are likely to be concerned about. In this regard, nanotechnology is similar to 'general purpose technologies', such as plastics, and perceived risks and value judgements need to be associated with specific applications rather than nano in general33. Furthermore, it has been argued that what we think of as 'the public' is also extraordinarily diverse, and that it would be folly to overlook this heterogeneity when formulating approaches to risk communication51. Therefore, engagement exercises that focus on specific product types! , industrial sectors or cultural demographics may stand a better chance of exploring public concerns related to that specific area of interest33. Such a targeted approach is particularly important for the food and farming industries, given that technological innovations in these areas have been contentious in the past43. Although there have been very few food-specific nanotechnology public engagement initiatives, the gradual expansion of the nanofoods market in recent years has prompted government bodies, in particular, to begin acknowledging the value of such activities. For instance, in 2009, the United Nations Food and Agriculture Organization and the World Health Organization stated that government authorities can build trust and contribute to constructive stakeholder dialogues by fostering "greater public confidence through institutional efforts to provide thorough oversight of applications of nanotech in food and packaging that are transparent and allow public involvement"52. Furthermore, the Nanotechnology Engagement Group, established in 2005 to document results from nanotechnology-related public engagement exercises and funded by the European Union, has recommended that government agencies promote transparency by creating maps to show how responsibilities for the regulation and ! funding of nanoscience are distributed, and by being open about uncertainties in science and science policy49. The group also urged decision-making bodies to train and mentor staff who can be involved in public engagement activities. The need for government agencies to make existing safety studies more accessible to the general public, while being sensitive to confidential business information, has also been pointed out43. In line with these recommendations, government bodies in the United States and elsewhere have made a conscious effort to engage the public about nanofoods, primarily by communicating information related to health and environmental safety. Uncertainties surrounding toxicity and the extent to which nanoparticles incorporated within plastics can migrate into contacted foods or the environment, all constitute scientific data gaps that need to be addressed to improve risk assessments53, 54, 55, 56, and regulatory agencies have pledged to continually update the public on how these risks are being managed. For example, on its website the US Food and Drug Administration (FDA) states that it "recognizes the importance of public engagement in developing a regulatory strategy for products containing nanoscale material and seeks to include the public at all stages of the process,"57 and it subsequently convened a Nanotechnology Task Force to discuss the regulation of nanotechnology ! products under its jurisdiction (in a process that included two public meetings). In its final report58, the task force recommended that the FDA "seek public input on the adequacy of FDA's policies and procedures," provide guidance that "would give affected manufacturers and other interested parties timely information about FDA's expectations, so as to foster predictability in the agency's regulatory processes, thereby enabling innovation and enhancing transparency, while protecting the public health," and "consider appropriate vehicles for communicating with the public about the use of nanoscale materials in FDA-regulated products". The first FDA guidance document, published in draft form in June 2011 (ref. 59), considers whether a FDA-regulated product contains nanomaterials or otherwise involves the use of nanotechnology. Over time, the agency plans to issue more specific guidance tailored to particular products or classes of products. Similar documents have also been published by the European Food Safety Authority60, and European governments have been active in their efforts to directly communicate with the public about nanofoods. In the UK, for example, in response to a recommendation in a report by the House of Lords Science and Technology Committee18, the Food Standards Agency held the first meeting of the Nanotechnologies and Food Discussion Group on 13 January 2011. Government bodies have also contributed to public engagement exercises by making resources available to universities and other non-government organizations. In the United States, for instance, the National Institute for Food and Agriculture (NIFA), which is part of the US Department of Agriculture, has funded projects to probe public opinion and study new ways of conducting an efficient dialogue with the public about food and agriculture applications of nanotechnology. One of these grants funds workshops to inform "public knowledge of emerging applications of agrifood nanotechnologies, and inform agrifood policymakers of local-level perceptions of and responses to them, with the overall goal of facilitating more 'socially responsive' agrifood nanotechnologies". Researchers funded by a separate NIFA grant plan to produce a series of audio and video programmes related to nanofoods in collaboration with Earth & Sky (a radio show that reaches millions of people daily) that w! ill be broadcast as a part of their regular programming and used in travelling museum exhibits. NIFA's higher education programme also supports curriculum development and graduate fellowship programmes in the area of food nanotechnology, and has also produced multimedia materials on various food- and agriculture-related applications of nanotechnology. What industry can do * Fearing the unnatural * What governments are doing * What industry can do * Media matters * Outlook * References * Acknowledgements * Author information Although government agencies take the lead in engaging the public about the health and environmental risks related to nanofoods, it may prove difficult for regulators to overtly incorporate public concerns related to ethical and social issues into their official public engagement activities, because such issues typically are not within the scope of their statutorily defined regulatory territory. In the United States, for example, the Federal Food, Drug and Cosmetic Act specifies that the FDA shall authorize the use of a food ingredient or packaging material unless a fair evaluation of the data either fails to show that the proposed use of the compound is safe or shows that the proposed use would promote deception of the consumer61. Safety is defined as reasonable certainty in the minds of competent scientists that the substance is not harmful under the intended conditions of use62, 63. The FDA has recognized that effective communication with the public about what it is doing! in this regard is an important aspect of ensuring the safe use of FDA-regulated products64, 65, but its statutory authority does not allow for the evaluation of the ethical or social ramifications of an intended use when evaluating the safety of food ingredients or packaging materials. As a result of these considerations, industry groups may be better candidates to enforce values-based governance and to drive public dialogues about the perceived ethical and social risks of nanofoods (for example, engineering of living matter, improvement of human abilities, privacy, naturalness of the food supply, and so on). Unfortunately, there is a prevailing opinion among food companies that, owing to the high cost and difficulty of engaging with the public, the rapid commercialization of beneficial products will be more effective at producing positive public perceptions66. In other words, food companies often view public engagement activities as a means of informing the public about the benefits of new products rather than of discussing the public's concerns66, which is a continuation of the now discredited belief that negative attitudes to science and technology are due to a knowledge deficit67. The International Risk Governance Council, an organization jointly funde! d by government and industry, reported recently that "the food industry in particular lacks a proactive communication strategy to deal with the public's need for more information concerning nanofoods," and warned that "without being more open about what they do and what they know, food companies are likely to be exposed to growing concerns, rumours and distrust"44. The House of Lords Science and Technology Committee in the UK came to a similar conclusion in its report18: "far from being transparent about its activities," they pointed out, "the food industry was refusing to talk about its work in [nanotechnology] ... This is exactly the type of behaviour which may bring about the public reaction which [industry] is trying to avert." Although the food industry has a vital role when it comes to interacting with the public about nanofoods, it has so far remained relatively uninvolved. The Centre for Business Relationships, Accountability, Sustainability and Society at Cardiff University points out that corporate social responsibility is currently interpreted by industry as "doing no harm," and that industry formulates risk-management policy as a reaction to government regulations rather than from a need to anticipate potential future impacts of their products66. Numerous academic, government and non-government organizations have urged the food industry to abandon this philosophy and adopt a more proactive approach to anticipating public concerns and building public trust by: * Using trade associations as a unified voice that can address fundamental, deep-rooted social concerns about nanofoods while protecting the images of individual corporations52. * Dedicating more resources to training and practice in risk management to prevent unnecessary secrecy, opaque behaviour and unprofessional risk-communication strategies having a negative impact on trust and public credibility44. * Collaborating with social scientists to define naturalness in the context of nanofoods and to determine which consumer demographics are more likely to be sensitive to this issue, because apprehension towards nanofoods derives significantly from uncertainty about the naturalness of such products32, 39. Proactive research programmes related to how future nanofoods products or regulatory decisions may impact public perceptions would also be helpful. * Actively participating in the formulation and delivery of public engagement exercises instead of relying on programme reports or summaries after the fact. This would allow the industry to respond more effectively to public concerns raised during these activities49. * Establishing an enforceable, transparent and inclusive process of self-regulation through a comprehensive, universal voluntary code of conduct that would not only encourage open cooperation with governments to address the physical risks of nanofoods, but also take ethical and social concerns, and regional or cultural sensitivities into consideration when developing or marketing new products44. "Public engagement should be treated as an investment in the future; building dividends takes time, patience and persistence." Adoption of any or all of these suggestions could help the food industry to prevent the public's downstream concerns related to nanofoods from becoming a source of dread, distrust and ultimately rejection. That said, it is important for all stakeholders to take a long-term view of their public outreach activities, and to not abandon trust-building or engagement efforts if they do not yield immediate public support for marketable nanotechnologies. Rather, public engagement should be treated as an investment in the future; building dividends takes time, patience and persistence. Media matters * Fearing the unnatural * What governments are doing * What industry can do * Media matters * Outlook * References * Acknowledgements * Author information © ISTOCKPHOTO.COM/ ALEXGUMEROV Government agencies have made a conscious effort to engage the public in discussions about nanofoods. The media has the power to enhance or undermine the efforts by the food industry or governments to engage the public about nanofoods, because of its role as a public information nexus. As a result, nanofoods stakeholders need to be especially cognizant of how the media is responding to developments in the field and adjust their public communication strategies accordingly. In 2011, Dudo et al. published the first analysis of journalistic nanotechnology coverage dealing specifically with nanofoods, and concluded that US newspaper articles have historically offered equitable treatment of the risks and benefits of food nanotechnology68. Nevertheless, media reporting of nanofoods issues is sure to continue evolving. Owing in part to a reduction in the number of journalists dedicated specifically to science reporting, Dudo et al. predict that future journalistic coverage of food nanotechnology is "likely to become even more event-driven and devoid of the more thoughtful treatmen! ts that specialist reporters are able to provide". Moreover, an increasing journalistic focus on safety or ethical concerns, or on news about regulatory gaps or industry silence about product development, could irrevocably damage public trust and lessen the effectiveness of future engagement initiatives68. The Dudo et al. study is an admirable first step in trying to understand how the media is influencing public opinion of nanofoods, but it is limited to newspaper coverage and does not consider other sources of information such as Wikipedia, YouTube, podcasts and blogs. Though some researchers have suggested that online news formats may help slow down or even reverse the widening knowledge gap between socio-economic demographics69, the Nanotechnology Engagement Group has warned that "as news media becomes more self-selectively personalized, readers will be even more able to ignore information that contrasts with pre-existing judgements: a self-sustaining cycle of one-sided information"49. Clearly, research is needed to understand how these new types of media sources influence public perceptions of risk, and stakeholders in nanofoods need to include these new media in their risk-communication strategies. Furthermore, a significant hurdle faced by stakeholders in any new technology is the silence of knowledgeable scientists, doctors, engineers and other experts in the wake of a breaking news story. Institutional restrictions on independent engagement with the media has been cited as a serious problem52, because breaking news stories are often biased by the collective voices of individuals and organizations with extreme agendas and a sophisticated knowledge of how to capitalize on media opportunities. Recognizing this issue, the Food and Agriculture Organization and the World Health Organization have jointly advocated the concept of a Science Media Centre, an independent, agenda-free organization that "works to get evidence-based science and credible scientists into the news media, at a time when society needs them most"52. A centre dedicated specifically to food-related media interactions would be immensely valuable to stakeholders in nanofoods as a means of injecting rel! iable and factual information into media treatments of the subject and ensuring that a vocal minority does not tip public sentiment in the direction of irrational fears. Outlook * Fearing the unnatural * What governments are doing * What industry can do * Media matters * Outlook * References * Acknowledgements * Author information "Mishandling of previous food technology debates has put nanofoods at a disadvantage by conditioning the public to distrust the food industry and the oversight system responsible for regulating it." The future prospects of nanofoods are far from certain. In one sense, the mishandling of previous food technology debates (such as GMOs) has put nanofoods at a disadvantage by conditioning the public to distrust the food industry and the oversight system responsible for regulating it. On the other hand, the history of agricultural biotechnology has taught some lessons about the value of clear communication and respecting public opinion, which many organizations are heeding. A commendable effort has been made by many stakeholders to engage with the public upstream of significant marketing of nanoproducts, although some researchers have suggested that a continued over-reliance on traditional engagement methods and educational tools (such as museum exhibits) will risk leaving the less-wealthy and less-educated citizens without crucial information about nanoscience and, ultimately, without a voice on policy issues69. However, public engagement initiatives of any type were almost! completely absent during the early stages of GMO development and commercialization, so nanotechnology in general appears to be edging in the right direction. Nanofoods stakeholders may be pleased to learn of recent work demonstrating that consumers are perhaps more willing to eat foods produced with nanomaterials than identical varieties that have been genetically engineered70, indicating that the proactive approach to interacting with the public about nanotechnology may be paying dividends. Nevertheless, as the nanofoods market expands, it is an open question whether media coverage will continue to provide a balanced portrayal of the potential benefits and risks posed by the incorporation of engineered nanomaterials into food and food-related products, or whether a gradual change to exaggerated headlines will lead to ripple effects that endanger not only the future of nanofoods, but also the future of nanotechnology as a whole. What ultimately happens will largely depend on how well we continue to research what drives consumer perceptions and adjust our approach to public engagement in the wake of past failures. 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McCarthy for helpful discussions, and library staff at the US Food and Drug Administration Center for Food Safety and Nutrition for consultations and assistance with literature searches. Author information * Fearing the unnatural * What governments are doing * What industry can do * Media matters * Outlook * References * Acknowledgements * Author information Affiliations * Timothy V. Duncan is at the US Food and Drug Administration, Institute for Food Safety and Health, Bedford Park, Illinois 60501-1957, USA Corresponding author Correspondence to: * Timothy V. Duncan Author Details * Timothy V. Duncan Contact Timothy V. Duncan Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Our choice from the recent literature
- Nat Nanotechnol 6(11):689 (2011)
Article preview View full access options Nature Nanotechnology | Research Highlights Our choice from the recent literature Journal name:Nature NanotechnologyVolume: 6,Page:689Year published:(2011)DOI:doi:10.1038/nnano.2011.200Published online04 November 2011 Science334 213–216, (2011) © 2011 AAAS Alkanes are a major constituent of natural gas and petroleum, but are one of the least chemically reactive classes of organic compounds. As a result, it can be difficult to convert them directly into more useful chemicals in a controlled manner. Gerhard Erker, Harald Fuchs, Lifeng Chi and colleagues at the University of Münster have now shown that a gold surface can be used to carry out precise polymerization reactions of linear alkanes. Article preview Read the full article * Instant access to this article: US$32 Buy now * Subscribe to Nature Nanotechnology for full access: Subscribe * Personal subscribers: Log in Additional access options: * Login via Athens * Login via your Institution * Purchase a site license * Use a document delivery service * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Author information Article tools * Print * Email * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Additional data - Cavity optomechanics: Mechanical memory sees the light
- Nat Nanotechnol 6(11):690-691 (2011)
Article preview View full access options Nature Nanotechnology | News and Views Cavity optomechanics: Mechanical memory sees the light * Garrett D. Cole1 * Markus Aspelmeyer1 * Affiliations * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:690–691Year published:(2011)DOI:doi:10.1038/nnano.2011.199Published online04 November 2011 A nanomechanical beam coupled to an optical cavity can be operated as a non-volatile memory element. Subject terms: * NEMS Article preview Read the full article * Instant access to this article: US$18 Buy now * Subscribe to Nature Nanotechnology for full access: Subscribe * Personal subscribers: Log in Additional access options: * Login via Athens * Login via your Institution * Purchase a site license * Use a document delivery service * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Author information Article tools * Print * Email * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * Garrett D. Cole and Markus Aspelmeyer are at the Vienna Center for Quantum Science and Technology VCQ, Faculty of Physics, University of Vienna, Austria Corresponding author Correspondence to: * Markus Aspelmeyer Author Details * Garrett D. Cole Search for this author in: * NPG journals * PubMed * Google Scholar * Markus Aspelmeyer Contact Markus Aspelmeyer Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Nanoelectronics: Shuttle transport for single electrons
- Nat Nanotechnol 6(11):691-692 (2011)
Article preview View full access options Nature Nanotechnology | News and Views Nanoelectronics: Shuttle transport for single electrons * Markus Kindermann1Journal name:Nature NanotechnologyVolume: 6,Pages:691–692Year published:(2011)DOI:doi:10.1038/nnano.2011.194Published online04 November 2011 A surface acoustic wave can be used to remove a single electron from a quantum dot, drag it along a nanowire, and deposit it in a second quantum dot. Subject terms: * Electronic properties and devices Article preview Read the full article * Instant access to this article: US$18 Buy now * Subscribe to Nature Nanotechnology for full access: Subscribe * Personal subscribers: Log in Additional access options: * Login via Athens * Login via your Institution * Purchase a site license * Use a document delivery service * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Author information Article tools * Print * Email * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * Markus Kindermann is in the School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA Corresponding author Correspondence to: * Markus Kindermann Author Details * Markus Kindermann Contact Markus Kindermann Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Nanomedicine: Gold nanowires to mend a heart
- Nat Nanotechnol 6(11):692-693 (2011)
Article preview View full access options Nature Nanotechnology | News and Views Nanomedicine: Gold nanowires to mend a heart * Marisa E. Jaconi1Journal name:Nature NanotechnologyVolume: 6,Pages:692–693Year published:(2011)DOI:doi:10.1038/nnano.2011.195Published online04 November 2011 Incorporating gold nanowires into porous alginate scaffolds can improve the conductivity of engineered heart patches made from these materials. Subject terms: * Nanomaterials * Nanomedicine Article preview Read the full article * Instant access to this article: US$18 Buy now * Subscribe to Nature Nanotechnology for full access: Subscribe * Personal subscribers: Log in Additional access options: * Login via Athens * Login via your Institution * Purchase a site license * Use a document delivery service * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Author information Article tools * Print * Email * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * Marisa E. Jaconi is in the Department of Pathology and Immunology, Faculty of Medicine, University of Geneva, Geneva, Switzerland Corresponding author Correspondence to: * Marisa E. Jaconi Author Details * Marisa E. Jaconi Contact Marisa E. Jaconi Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Nanoparticle devices: Going with the electron flow
- Nat Nanotechnol 6(11):693-694 (2011)
Article preview View full access options Nature Nanotechnology | News and Views Nanoparticle devices: Going with the electron flow * Xi Yu1 * Vincent M. Rotello1 * Affiliations * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:693–694Year published:(2011)DOI:doi:10.1038/nnano.2011.192Published online04 November 2011 Electric currents can be steered by coupling the flow of electrons and ions in films of gold nanoparticles coated with ionic ligands. Subject terms: * Electronic properties and devices * Nanoparticles Article preview Read the full article * Instant access to this article: US$18 Buy now * Subscribe to Nature Nanotechnology for full access: Subscribe * Personal subscribers: Log in Additional access options: * Login via Athens * Login via your Institution * Purchase a site license * Use a document delivery service * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Author information Article tools * Print * Email * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * Xi Yu and Vincent M. Rotello are at the Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003, USA Corresponding author Correspondence to: * Vincent M. Rotello Author Details * Xi Yu Search for this author in: * NPG journals * PubMed * Google Scholar * Vincent M. Rotello Contact Vincent M. Rotello Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Electron microscopy of specimens in liquid
- Nat Nanotechnol 6(11):695-704 (2011)
Nature Nanotechnology | Review Electron microscopy of specimens in liquid * Niels de Jonge1 * Frances M. Ross2 * Affiliations * Corresponding authorsJournal name:Nature NanotechnologyVolume: 6,Pages:695–704Year published:(2011)DOI:doi:10.1038/nnano.2011.161Published online23 October 2011 Abstract * Abstract * Author information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Imaging samples in liquids with electron microscopy can provide unique insights into biological systems, such as cells containing labelled proteins, and into processes of importance in materials science, such as nanoparticle synthesis and electrochemical deposition. Here we review recent progress in the use of electron microscopy in liquids and its applications. We examine the experimental challenges involved and the resolution that can be achieved with different forms of the technique. We conclude by assessing the potential role that electron microscopy of liquid samples can play in areas such as energy storage and bioimaging. View full text Subject terms: * Nanobiotechnology * Nanomaterials * Nanometrology and instrumentation Figures at a glance * Figure 1: Configurations for electron microscopy in liquid. , TEM imaging with an open environmental chamber containing liquid and vapour. Differential apertures separate the microscope vacuum from the higher pressure at the sample. , SEM imaging with an environmental chamber. The electron beam scans in x and y directions over the sample. , TEM imaging of nanoparticles in a liquid fully enclosed between electron transparent windows. , STEM imaging in a fully enclosed liquid, used to image nanoparticle labels on whole biological cells. , SEM of a liquid sample under an electron transparent window. , Combination of SEM and light microscopy of a liquid sample above an electron transparent window. * Figure 2: Examples of electron microscopy systems for liquids. , Fabrication of a liquid cell from Si microchips (upper and lower wafers) with SiN windows, glass reservoirs, lids and three electrodes for electrochemical TEM experiments3. , Photograph of an assembled liquid cell. , A single Si microchip with an electron transparent SiN window25. The dimensions of the microchip are 2.0 × 2.3 × 0.3 mm. , A microfluidic chamber formed from two of the microchips in , showing the liquid flow direction. , A capsule with an electron transparent window for imaging liquid samples in SEM43. The outer diameter is 16 mm. , Cell culture dish with a microchip with a SiN window33, for combined light microscopy and SEM. , The back (vacuum) side of the microchip for the culture dish. Panels reproduced with permission from: , ref. 3, © 2003 NPG; , ref. 25, © 2010 CUP; , ref. 43, © 2004 Informa Healthcare; , ref. 33, © 2010 Elsevier. Panel modified with permission from ref. 4, © 2009 National Academy of Sciences. * Figure 3: Electron microscopy of biological samples. a, Human monocyte-derived macrophages imaged with SEM in a wet environment39 at 4.9 torr and 7 °C. Samples were fixed in glutaraldehyde and rinsed with deionized water before imaging. , SEM image of H. pylori bacterium fully immersed in liquid, imaged using a capsule with a thin window. Samples were incubated with complexed biotinylated gastrin on streptavidin-coated 20 nm Au particles, followed by glutaraldehyde fixation. , STEM image of Au-labelled epidermal growth factor receptors on whole fixed COS7 fibroblast cells in liquid. The Au labels are visible as yellow spots on the light blue cellular material. The background shows in dark blue. , Endocytotic vesicles were formed in a second sample after a longer incubation. , Fluorescence microscopy image of COS7 cells33. The cells were fixed, labelled with a fluorescent dye, and stained for contrast in SEM. , SEM image of the cellular material in the rectangle in imaged under fully hydrated conditions33. Panels reproduced wi! th permission from: , ref. 39, © 2009 Wiley; , ref. 33, © 2010 Elsevier. Panels modified with permission from: , ref. 2, © 2004 National Academy of Sciences; , ref. 4, © 2009 National Academy of Sciences. * Figure 4: Liquid cell electron microscopy in materials science. , Images and electrochemical data obtained during potentiostatic deposition of Cu on a polycrystalline Au electrode from 0.1M CuSO4/0.18M H2SO4. Cu has dark contrast whereas the Au (20 nm thick), SiN windows (80 nm thick) and electrolyte (1 μm thick) provide the grey background. The applied potential was −70 mV with respect to a Cu reference electrode, and the graph shows the total current versus time. The electrode area is 2 × 10−5 cm2. Red lines show the times of each image. , Images acquired during Pt nanoparticle formation from a solution containing 10 mg mL−1 Pt(acetylacetonate)2 in a 9:1 mixture of o-dichlorobenzene and oleylamine. The images were recorded after 17.9, 18.7, and 22.3 s of beam exposure during which a coalescence event occurs. The graph shows the size of this (red circles) and another particle that appears to grow by addition of monomers (blue triangles). , Energy filtered images at 16 s intervals during dendritic growth of Cu from the edge of an! electrode6. Galvanostatic conditions were used with current density 40 mA cm−2 and average lateral growth rate 0.2 μm s−1. Panels modified with permission from: , ref. 52, © 2006 ACS; , ref. 6, © 2009 AAAS; , ref. 104 © 2010 CUP. * Figure 5: Resolution of different forms of electron microscopy in liquid. Theoretical maximal resolution versus water thickness for TEM, STEM and SEM. The resolution was calculated for typical TEM and STEM instrument parameters at 200 keV beam energy (see text), and for the imaging of Au nanoparticles at the bottom of a layer of water for TEM, and at the top of the layer for STEM. The resolution obtained in SEM just below the liquid-enclosing membrane does not depend on the liquid thickness (see text). Experimental data points are shown for Au nanoparticles in TEM31, STEM26 and SEM with a 30-nm-thick SiN window33, and for PbS nanoparticles in water imaged with STEM35. The error bars represent experimental errors. Author information * Abstract * Author information Affiliations * Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 2215 Garland Avenue, Nashville, Tennessee 37232, USA * Niels de Jonge * IBM T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, New York 10598, USA * Frances M. Ross Competing financial interests The authors declare no competing financial interests. Corresponding authors Correspondence to: * Niels de Jonge or * Frances M. Ross Author Details * Niels de Jonge Contact Niels de Jonge Search for this author in: * NPG journals * PubMed * Google Scholar * Frances M. Ross Contact Frances M. Ross Search for this author in: * NPG journals * PubMed * Google Scholar Additional data - Ambipolar field effect in the ternary topological insulator (BixSb1–x)2Te3 by composition tuning
- Nat Nanotechnol 6(11):705-709 (2011)
Nature Nanotechnology | Letter Ambipolar field effect in the ternary topological insulator (BixSb1–x)2Te3 by composition tuning * Desheng Kong1, 6 * Yulin Chen2, 3, 4, 6 * Judy J. Cha1 * Qianfan Zhang1 * James G. Analytis2, 4 * Keji Lai2, 3 * Zhongkai Liu2, 3, 4 * Seung Sae Hong2 * Kristie J. Koski1 * Sung-Kwan Mo5 * Zahid Hussain5 * Ian R. Fisher2, 4 * Zhi-Xun Shen2, 3, 4 * Yi Cui1, 4 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:705–709Year published:(2011)DOI:doi:10.1038/nnano.2011.172Received22 August 2011Accepted13 September 2011Published online02 October 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Topological insulators exhibit a bulk energy gap and spin-polarized surface states that lead to unique electronic properties1, 2, 3, 4, 5, 6, 7, 8, 9, with potential applications in spintronics and quantum information processing. However, transport measurements have typically been dominated by residual bulk charge carriers originating from crystal defects or environmental doping10, 11, 12, and these mask the contribution of surface carriers to charge transport in these materials. Controlling bulk carriers in current topological insulator materials, such as the binary sesquichalcogenides Bi2Te3, Sb2Te3 and Bi2Se3, has been explored extensively by means of material doping8, 9, 11 and electrical gating13, 14, 15, 16, but limited progress has been made to achieve nanostructures with low bulk conductivity for electronic device applications. Here we demonstrate that the ternary sesquichalcogenide (BixSb1–x)2Te3 is a tunable topological insulator system. By tuning the ratio of bi! smuth to antimony, we are able to reduce the bulk carrier density by over two orders of magnitude, while maintaining the topological insulator properties. As a result, we observe a clear ambipolar gating effect in (BixSb1–x)2Te3 nanoplate field-effect transistor devices, similar to that observed in graphene field-effect transistor devices17. The manipulation of carrier type and density in topological insulator nanostructures demonstrated here paves the way for the implementation of topological insulators in nanoelectronics and spintronics. View full text Subject terms: * Electronic properties and devices * Nanomagnetism and spintronics * Nanomaterials * Synthesis and processing Figures at a glance * Figure 1: (BixSb1–x)2Te3, a tunable topological insulator system with a single Dirac cone of surface states. , Tetradymitetype-type crystal structure of (BixSb1–x)2Te3 consists of quintuple layers (thickness, ~1 nm) bonded by van der Waals interactions. , ARPES Fermi surface maps (top row) and band dispersions along K-Γ-M (bottom row) directions for bulk single crystals with nominal compositions of Bi2Te3, (Bi0.75Sb0.25)2Te3, (Bi0.50Sb0.50)2Te3, (Bi0.25Sb0.75)2Te3 and Sb2Te3. By increasing the concentration of antimony, EF exhibits a systematic downshift from the BCB to the BVB through a bulk insulating state achieved in (Bi0.5Sb0.5)2Te3. The SSB consists of a single Dirac cone around the Γ point, forming a hexagram Fermi surface (top row) and V-shaped dispersion in the band structure (bottom row). The apex of the V-shaped dispersion is the Dirac point. Note that the shape of the Dirac cone (especially the geometry below the Dirac point, which hybridizes with the BVB) also varies with bismuth/antimony composition. For a bismuth:antimony ratio less than 50:50, as-grown materials! become p-type; EF resides below the Dirac point, so only the lower part of the Dirac cone is revealed in the ARPES measurement (and the V-shaped dispersion inside the bulk gap is not seen). The n-type SSB pocket on the Fermi surface shrinks with increasing antimony concentration and eventually becomes a p-type pocket hybridized with the bulk band (BVB) in bismuth:antimony concentrations of 25:75 and 0:100. , Three-dimensional illustration of the band structure of (Bi0.50Sb0.50)2Te3 with vanished bulk states on the Fermi surface. SSB forms a single Dirac cone with hexagram Fermi surface. , Ab initio band structure calculations of Bi2Te3, (Bi0.75Sb0.25)2Te3, (Bi0.50Sb0.50)2Te3, (Bi0.25Sb0.75)2Te3 and Sb2Te3 show qualitative agreement with ARPES measurements (, bottom row), with gapless SSB consist of linear dispersions spanning the bulk gap observed in all the compositions. The difference in EF between calculated and measured band structures reflects the carriers arising fro! m defects and vacancies in the crystals. * Figure 2: Characterization of (BixSb1–x)2Te3 nanoplates. , Optical microscopy image of vapour–solid grown (Bi0.50Sb0.50)2Te3 nanoplates. , High-resolution TEM image of the edge of a (Bi0.50Sb0.50)2Te3 nanoplate (shown in the inset) reveals clear crystalline structure with top and bottom surfaces as (0001) atomic planes. , SAED pattern with sharp diffraction spots indicates that the nanoplate is a high-quality, single crystal. , Bismuth, antimony and tellurium elemental maps obtained from an EDX scan. Overlaying the elemental maps (bottom right panel) reveals the morphology of the nanoplate, indicating that the elements are fairly uniformly distributed without obvious precipitates. , Composition xEDX in (BixSb1–x)2Te3 nanoplates calibrated by EDX spectra. , Nanoplate area carrier density is chemically modulated by adjusting compositions, as determined by the Hall effect. Average carrier concentration from multiple samples is shown as filled circles. Error bars correspond to maximum deviation. Inset: schematic of device structur! e. * Figure 3: Ambipolar field effect in ultrathin nanoplates of (BixSb1–x)2Te3. , Typical dependence of resistance R on gate voltage VG in an ultrathin (Bi0.50Sb0.50)2Te3 nanoplate (thickness, ~5 nm) exhibiting a sharp peak in the resistance and subsequent decay. Inset: optical microscopy image of FET device with a thickness of ~5 nm as determined by AFM. , High-field Hall coefficient RH versus VG for the same nanoplate. Each RH (solid circle) is extracted from the Hall trace for ±6 T at a certain VG. At the VG at peak R, RH exhibits a reversal in sign. * Figure 4: Temperature-dependent field effect in (BixSb1–x)2Te3 nanoplates. , Dependence of resistance R and Hall coefficient RH on gate voltage VG for a 5-nm-thick (Bi0.50Sb0.50)2Te3 nanoplate (inset), showing the ambipolar field effect. For Hall effect measurements, filled circles indicate high-field Hall coefficient extracted from Hall traces for ±6 T at specific VG. The curve is obtained by measuring the Hall resistance versus VG at magnetic fields of ±4 T. ,, Temperature dependence of R at different VG from electron conductor to mixed state () and hole conductor to mix state (). R is normalized to its value at the highest measured temperature. , Dependence of resistance R and Hall coefficient RH on gate voltage VG for a 9-nm-thick (Bi0.50Sb0.50)2Te3 nanoplate (inset). The Hall coefficient is obtained by measuring the Hall resistance versus VG at magnetic fields of ±4 T. ,, Temperature dependence of R at different VG. R is normalized to the value at the highest measured temperature. Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Desheng Kong & * Yulin Chen Affiliations * Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA * Desheng Kong, * Judy J. Cha, * Qianfan Zhang, * Kristie J. Koski & * Yi Cui * Department of Applied Physics, Stanford University, Stanford, California 94305, USA * Yulin Chen, * James G. Analytis, * Keji Lai, * Zhongkai Liu, * Seung Sae Hong, * Ian R. Fisher & * Zhi-Xun Shen * Department of Physics, Stanford University, Stanford, California 94305, USA * Yulin Chen, * Keji Lai, * Zhongkai Liu & * Zhi-Xun Shen * Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA * Yulin Chen, * James G. Analytis, * Zhongkai Liu, * Ian R. Fisher, * Zhi-Xun Shen & * Yi Cui * Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA * Sung-Kwan Mo & * Zahid Hussain Contributions D.K., Y.L.C. and Y.C. conceived the experiments. Y.L.C. and Z.K.L. carried out ARPES measurements. J.G.A. synthesized and characterized bulk single crystals. Q.F.Z. performed electronic structure calculations. D.K. and J.J.C. carried out synthesis, structural characterization and device fabrication for nanoplates. D.K., K.L., J.J.C., S.S.H. and K.J.K. carried out transport measurements and analyses. All authors contributed to the scientific planning and discussions. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Yi Cui Author Details * Desheng Kong Search for this author in: * NPG journals * PubMed * Google Scholar * Yulin Chen Search for this author in: * NPG journals * PubMed * Google Scholar * Judy J. Cha Search for this author in: * NPG journals * PubMed * Google Scholar * Qianfan Zhang Search for this author in: * NPG journals * PubMed * Google Scholar * James G. Analytis Search for this author in: * NPG journals * PubMed * Google Scholar * Keji Lai Search for this author in: * NPG journals * PubMed * Google Scholar * Zhongkai Liu Search for this author in: * NPG journals * PubMed * Google Scholar * Seung Sae Hong Search for this author in: * NPG journals * PubMed * Google Scholar * Kristie J. Koski Search for this author in: * NPG journals * PubMed * Google Scholar * Sung-Kwan Mo Search for this author in: * NPG journals * PubMed * Google Scholar * Zahid Hussain Search for this author in: * NPG journals * PubMed * Google Scholar * Ian R. Fisher Search for this author in: * NPG journals * PubMed * Google Scholar * Zhi-Xun Shen Search for this author in: * NPG journals * PubMed * Google Scholar * Yi Cui Contact Yi Cui Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (1,025 KB) Supplementary information Additional data - Step-like enhancement of luminescence quantum yield of silicon nanocrystals
- Nat Nanotechnol 6(11):710-713 (2011)
Nature Nanotechnology | Letter Step-like enhancement of luminescence quantum yield of silicon nanocrystals * D. Timmerman1 * J. Valenta2 * K. Dohnalová1 * W. D. A. M. de Boer1 * T. Gregorkiewicz1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:710–713Year published:(2011)DOI:doi:10.1038/nnano.2011.167Received21 July 2011Accepted09 September 2011Published online09 October 2011Corrected online21 October 2011 Abstract * Abstract * Change history * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Carrier multiplication by generation of two or more electron–hole pairs following the absorption of a single photon may lead to improved photovoltaic efficiencies1 and has been observed in nanocrystals made from a variety of semiconductors, including silicon. However, with few exceptions2, these reports have been based on indirect ultrafast techniques3, 4, 5, 6. Here, we present evidence of carrier multiplication in closely spaced silicon nanocrystals contained in a silicon dioxide matrix by measuring enhanced photoluminescence quantum yield. As the photon energy increases, the quantum yield is expected to remain constant, or to decrease as a result of new trapping and recombination channels being activated. Instead, we observe a step-like increase in quantum yield for larger photon energies that is characteristic of carrier multiplication7. Modelling suggests that carrier multiplication is occurring with high efficiency and close to the energy conservation limit. View full text Subject terms: * Nanoparticles * Photonic structures and devices Figures at a glance * Figure 1: Experimental set-up for quantum yield determination. The excitation source (xenon lamp with monochromator, light-emitting diode (LED) or tunable optical parametric oscillator (OPO) laser system) excites the silicon nanocrystal sample placed inside the integrating sphere. Homogeneously scattered (within the sphere) emission and non-absorbed excitation light are guided by an ultraviolet-grade optical fibre to an imaging spectrometer and registered by a CCD detector. * Figure 2: Spectral dependence of external quantum yield of photoluminescence. Results for sample A, sample B, po-Si 1 and po-Si 2. The lower panels show multiples of the photoluminescence spectra of each sample (that is, the energy axis is multiplied by either 2 or 3, indicated by 2EPL and 3EPL, respectively). Black dashed lines, indicating the 'steps', serve only as a guide to the eye. * Figure 3: Effect of inter-nanocrystal separation. Spectral dependence of normalized external photoluminescence quantum yield for two samples with the same average nanocrystal size and distribution, but different concentrations. Red and black dashed lines serve as guides to the eye. Error bars represent experimental accuracy of quantum yield determination for different photon energies. * Figure 4: Photovoltaic impact. Comparison of carrier generation yield for bulk silicon (taken from ref. 32) with values of quantum yield for sample A and po-Si 2 (normalized to unity in the low-photon-energy regime). Thick red and blue semi-transparent lines are added as guides to the eye and can be reproduced very well using the carrier multiplication modelling developed in ref. 7 (see Supplementary Information). Standard reference solar spectra AM 1.5 and AM 0 (extraterrestrial) are indicated in green and light green, respectively. Change history * Abstract * Change history * Author information * Supplementary informationCorrected online 21 October 2011In the version of this Letter originally published online, the third sentence of the abstract should have read: "Here, we present evidence of carrier multiplication in closely spaced silicon nanocrystals contained in a silicon dioxide matrix by measuring enhanced photoluminescence quantum yield." This has been corrected in all versions of the Letter. Author information * Abstract * Change history * Author information * Supplementary information Affiliations * Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, The Netherlands * D. Timmerman, * K. Dohnalová, * W. D. A. M. de Boer & * T. Gregorkiewicz * Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, Prague 2, CZ-12116, Czech Republic * J. Valenta Contributions D.T. and T.G. conceived the project, co-wrote the paper and, together with J.V. and K.D., designed the experiments. D.T., J.V. and K.D. performed the experiments and contributed to data analysis. D.T. and K.D. prepared sputtered and po-Si materials, respectively. T.G. supervised the project. All authors discussed the results and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * D. Timmerman Author Details * D. Timmerman Contact D. Timmerman Search for this author in: * NPG journals * PubMed * Google Scholar * J. Valenta Search for this author in: * NPG journals * PubMed * Google Scholar * K. Dohnalová Search for this author in: * NPG journals * PubMed * Google Scholar * W. D. A. M. de Boer Search for this author in: * NPG journals * PubMed * Google Scholar * T. Gregorkiewicz Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Change history * Author information * Supplementary information PDF files * Supplementary information (2,768 KB) Additional data - Cell entry of one-dimensional nanomaterials occurs by tip recognition and rotation
- Nat Nanotechnol 6(11):714-719 (2011)
Nature Nanotechnology | Letter Cell entry of one-dimensional nanomaterials occurs by tip recognition and rotation * Xinghua Shi1, 4 * Annette von dem Bussche2 * Robert H. Hurt1, 3 * Agnes B. Kane2, 3 * Huajian Gao1, 3 * Affiliations * Contributions * Corresponding authorsJournal name:Nature NanotechnologyVolume: 6,Pages:714–719Year published:(2011)DOI:doi:10.1038/nnano.2011.151Received04 April 2011Accepted15 August 2011Published online18 September 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Materials with high aspect ratio, such as carbon nanotubes and asbestos fibres, have been shown to cause length-dependent toxicity in certain cells because these long materials prevent complete ingestion and this frustrates the cell1, 2, 3. Biophysical models have been proposed to explain how spheres and elliptical nanostructures enter cells4, 5, 6, 7, 8, but one-dimensional nanomaterials have not been examined. Here, we show experimentally and theoretically that cylindrical one-dimensional nanomaterials such as carbon nanotubes enter cells through the tip first. For nanotubes with end caps or carbon shells at their tips, uptake involves tip recognition through receptor binding, rotation that is driven by asymmetric elastic strain at the tube–bilayer interface, and near-vertical entry. The precise angle of entry is governed by the relative timescales for tube rotation and receptor diffusion. Nanotubes without caps or shells on their tips show a different mode of membrane i! nteraction, posing an interesting question as to whether modifying the tips of tubes may help avoid frustrated uptake by cells. View full text Subject terms: * Nanomaterials * Environmental, health and safety issues Figures at a glance * Figure 1: Experimental evidence for energy-dependent tip-entry mode in the cellular interactions of one-dimensional nanomaterials. –, Field-emission SEM images following fixation and osmium tetroxide staining. Scale bars, 300 nm. , Entry of MWCNTs into murine liver cells. Left: MWCNT undergoing high-angle tip entry. Middle: arrow shows carbon shell that distinguishes nanotubes from surface microvilli. Right: arrows show membrane invaginations at the point of entry, characteristic of endocytosis. , Isolated MWCNT (single arrow) and tube bundle (double arrow) entering human mesothelial cells at high angle. , Gold nanowires (30 nm, left) and 500 nm crocidolite asbestos fibre (right) entering mesothelial cells through their tips. , Reduced uptake at 4 °C (top) and in the presence of a metabolic inhibitor mixture (bottom) containing NaF, NaN3 and antimycin A. Error bars show standard error; asterisks indicate that the temperature and inhibitor effects are statistically significant (P < 0.0005 and 0.005, respectively), confirming energy-dependent endocytosis. * Figure 2: Course-grained molecular dynamics simulation model. Models of DPPC lipid and receptor molecules formed by one hydrophilic head-bead and two hydrophobic tail-beads, and a capped MWCNT with diameter d = 20 nm and length L = 46 nm consisting of three concentric walls. A membrane bilayer consisting of lipid and receptor molecules spans the simulation box. * Figure 3: Time sequence of CGMD simulation results showing a MWCNT penetrating the cell membrane at an initial entry angle of θ0 = 45°. , At receptor (green) density φ = 0.25, the MWCNT rotates to 90 before being fully wrapped. , At receptor density φ = 0.33, the tube is fully wrapped before reaching the 90 entry angle. , At receptor density φ = 1, the tube rotates towards a low entry angle. * Figure 4: Analytical model of a MWCNT entering cell. ,, Timescales associated with wrapping and tip rotation: entry time as a function of the engulfed length () under selected parameter values eRL = 15, B = 20, ξL = 5,000 µm−2, , d = 20 nm, D = 1 × 103 (red line) or 1 × 104 nm2 s−1 (blue line); evolution of the entry angle of the MWCNT () at different initial entry angles θ0 = 1°, 15°, 45° and 75°. The other parameters are d = 20 nm, L = Li + Le = 30 µm, ηe = 1 × 10−3 Pa s, ηi = 10 Pa s. Inset to : schematic of an MWCNT entering a cell at angle θ. The curved bilayer exerts torque T onto the MWCNT. , Total elastic energy as a function of the entry angle of the MWCNT relative to its reference value at the entry angle of 90°. The solid red line is a fit from CGMD simulation results (blue squares). Author information * Abstract * Author information * Supplementary information Affiliations * School of Engineering, Brown University, Providence, Rhode Island 02912, USA * Xinghua Shi, * Robert H. Hurt & * Huajian Gao * Department of Pathology and Laboratory Medicine, Brown University, Providence, Rhode Island 02912, USA * Annette von dem Bussche & * Agnes B. Kane * Institute for Molecular and Nanoscale Innovation, Brown University, Providence, Rhode Island, 02912, USA * Robert H. Hurt, * Agnes B. Kane & * Huajian Gao * Present address: State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China * Xinghua Shi Contributions X.H.S., A.v.d.B., R.H.H., A.B.K. and H.J.G. conceived and designed the experiments and simulations. X.H.S. performed the simulations. A.v.d.B. performed the experiments. X.H.S., A.v.d.B., R.H.H., A.B.K. and H.J.G. analysed the data. X.H.S., A.v.d.B., R.H.H., A.B.K. and H.J.G. co-wrote the paper. All authors discussed the results and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding authors Correspondence to: * Huajian Gao or * Agnes B. Kane Author Details * Xinghua Shi Search for this author in: * NPG journals * PubMed * Google Scholar * Annette von dem Bussche Search for this author in: * NPG journals * PubMed * Google Scholar * Robert H. Hurt Search for this author in: * NPG journals * PubMed * Google Scholar * Agnes B. Kane Contact Agnes B. Kane Search for this author in: * NPG journals * PubMed * Google Scholar * Huajian Gao Contact Huajian Gao Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (4,203 KB) Supplementary information Additional data - Nanowired three-dimensional cardiac patches
- Nat Nanotechnol 6(11):720-725 (2011)
Nature Nanotechnology | Letter Nanowired three-dimensional cardiac patches * Tal Dvir1, 2, 7 * Brian P. Timko1, 2, 7 * Mark D. Brigham3 * Shreesh R. Naik1 * Sandeep S. Karajanagi1, 4 * Oren Levy5, 6 * Hongwei Jin3 * Kevin K. Parker3 * Robert Langer1 * Daniel S. Kohane2 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:720–725Year published:(2011)DOI:doi:10.1038/nnano.2011.160Received20 May 2011Accepted19 August 2011Published online25 September 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Engineered cardiac patches for treating damaged heart tissues after a heart attack are normally produced by seeding heart cells within three-dimensional porous biomaterial scaffolds1, 2, 3. These biomaterials, which are usually made of either biological polymers such as alginate4 or synthetic polymers such as poly(lactic acid) (PLA)5, help cells organize into functioning tissues, but poor conductivity of these materials limits the ability of the patch to contract strongly as a unit6. Here, we show that incorporating gold nanowires within alginate scaffolds can bridge the electrically resistant pore walls of alginate and improve electrical communication between adjacent cardiac cells. Tissues grown on these composite matrices were thicker and better aligned than those grown on pristine alginate and when electrically stimulated, the cells in these tissues contracted synchronously. Furthermore, higher levels of the proteins involved in muscle contraction and electrical coupling! are detected in the composite matrices. It is expected that the integration of conducting nanowires within three-dimensional scaffolds may improve the therapeutic value of current cardiac patches. View full text Subject terms: * Nanomaterials * Nanomedicine Figures at a glance * Figure 1: Schematic overview of three-dimensional nanowire cardiac tissue. , Isolated cardiomyocytes are cultured in either pristine alginate or Alg–NW composites. Insets highlight the components of the engineered tissue: cardiac cells (red), alginate pore walls (blue) and gold nanowires (yellow). , Whereas cardiomyocytes in pristine alginate scaffolds (top) typically form only small clusters that beat asynchronously and with random polarization, Alg–NW scaffolds (bottom) can exhibit synchronization across scaffold walls, throughout the entire scaffold. , Cardiomyocytes cultured in alginate scaffolds (top) form small beating clusters, but synchronously beating cardiomyocytes in Alg–NW composites (bottom) have the potential to form organized cardiac-like tissue. Colours, contour lines and arrows represent the spatial and temporal evolution of the signal maximum. * Figure 2: Incorporation of nanowires within alginate scaffolds. ,, Transmission electron microscopy images of a typical distribution of gold nanowires, which exhibited an average length of ~1 µm and average diameter of 30 nm. ,, SEM revealed that the nanowires (1 mg ml−1) assembled within the pore walls of the scaffold into star-shaped structures with a total length scale of 5 µm. The assembled wires were distributed homogeneously within the matrix () at a distance of ~5 µm from one another (). * Figure 3: Increased electrical conductivity of alginate by incorporation of nanowires. , Spatial conductivity was measured by conductive probe atomic force microscopy (C-AFM). The ITO slide served a backside contact, and the conductive AFM probe was used to simultaneously measure surface topography and conductance through the film. , The equivalent circuit can be represented by capacitors (alginate) and resistors (nanowires) connected in parallel. , Topographic mapping revealed nanowires protruding from the composite alginate thin film (5 × 5 µm). , Spatial conductivity within the Alg–NW film as measured by C-AFM. Current spikes were measured at the location of the nanowires. , Current measured at the nanowires (red) increased with bias voltage over the range –1 to 1 V, while negligible current passed through nanowire-free regions of the alginate film (blue) over the same range. , Overall impedance of the scaffold biomaterial before and after modification with nanowires. Thin layers of Alg–NW or pure alginate films were pressed between two ITO glass sl! ides. These slides served as electrodes and were used to apply an a.c. bias with frequency swept between 1 MHz and 10 Hz. At frequencies near d.c., the impedance of the composite membrane was much lower than that of the pure film. * Figure 4: Cardiac cell organization within the three-dimensional scaffold. –, H&E stained thin sections of the engineered tissues on day 8 revealed a thick tissue in the nanowire scaffold (,), whereas the engineered tissue in the pristine scaffolds demonstrated non-continuous tissue separated by pore walls (,). , Nanowires are seen within the pore walls of a relatively empty region of a scaffold (black dots indicated by yellow arrows). , In a sparsely populated region, wires within the wall (black dots indicated by yellow arrows) were in close proximity to cell aggregates (red asterisks). ,, Immunostaining of the cell-seeded scaffolds on day 8 revealed pervasive troponin I expression (red) within the Alg–NW scaffold (), but less staining was observed in the aggregates in the unmodified scaffolds (). , Connexin 43 gap junction protein was found between cardiomyocytes in the nanowire-containing scaffolds (green dots indicated by white arrows). Nuclei are coloured in blue. , Quantification of connexin 43 protein expression by western blot. , Quant! ification of sarcomeric actinin protein expression by western blot. Scale bars, 200 µm (,) or 20 µm (,,–). * Figure 5: Calcium transient propagation within engineered tissues. Calcium transient was assessed at specified points (white circles) by monitoring calcium dye fluorescence (green). , Sites monitored in pristine scaffold, where site I is the stimulation point. , Calcium transients were only observed at the stimulation point in the unmodified scaffold. F/F0 refers to measured fluorescence normalized to background fluorescence. , Sites monitored in an Alg–NW scaffold. The stimulation point was 2 mm diagonally to the lower left of point I (that is, off the figure). The white arrow represents the direction of propagation. , Calcium transients were observed at all points. , Comparison of initial time courses of single signals from sites I–V in , Quantification of calcium transients (by relative fluorescence) from all samples (n = 6 in each group). Bars represent signal maximum transient 2 mm from the stimulation site (F2mm), normalized to the signal maximum at the stimulation site (Fstim). Scale bars in and , 100 µm. Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Tal Dvir & * Brian P. Timko Affiliations * Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA * Tal Dvir, * Brian P. Timko, * Shreesh R. Naik, * Sandeep S. Karajanagi & * Robert Langer * Laboratory for Biomaterials and Drug Delivery, Department of Anesthesiology, Division of Critical Care Medicine, Children's Hospital Boston, Harvard Medical School, 300 Longwood Avenue, Boston, Massachusetts 02115, USA * Tal Dvir, * Brian P. Timko & * Daniel S. Kohane * Disease Biophysics Group, Wyss Institute for Biologically-Inspired Engineering, School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA * Mark D. Brigham, * Hongwei Jin & * Kevin K. Parker * Department of Surgery, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114, USA * Sandeep S. Karajanagi * Harvard-Massachusetts Institute of Technology Division of Health Sciences and Technology, Cambridge, Massachusetts 02139, USA * Oren Levy * Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Cambridge, Massachusetts 02139, USA * Oren Levy Contributions T.D. and B.P.T. conceived the idea. T.D., B.P.T., K.K.P., R.L. and D.S.K. designed the experiments and interpreted the data. T.D., B.P.T., M.D.B., S.R.N., S.S.K. and O.L. performed the experiments. H.J. analysed data. T.D., B.P.T. and D.S.K. co-wrote the paper. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Daniel S. Kohane Author Details * Tal Dvir Search for this author in: * NPG journals * PubMed * Google Scholar * Brian P. Timko Search for this author in: * NPG journals * PubMed * Google Scholar * Mark D. Brigham Search for this author in: * NPG journals * PubMed * Google Scholar * Shreesh R. Naik Search for this author in: * NPG journals * PubMed * Google Scholar * Sandeep S. Karajanagi Search for this author in: * NPG journals * PubMed * Google Scholar * Oren Levy Search for this author in: * NPG journals * PubMed * Google Scholar * Hongwei Jin Search for this author in: * NPG journals * PubMed * Google Scholar * Kevin K. Parker Search for this author in: * NPG journals * PubMed * Google Scholar * Robert Langer Search for this author in: * NPG journals * PubMed * Google Scholar * Daniel S. Kohane Contact Daniel S. Kohane Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (900 KB) Supplementary information Movies * Supplementary information (7,661 KB) Supplementary movie 1 * Supplementary information (5,347 KB) Supplementary movie 2 Additional data - Dynamic manipulation of nanomechanical resonators in the high-amplitude regime and non-volatile mechanical memory operation
- Nat Nanotechnol 6(11):726-732 (2011)
Nature Nanotechnology | Article Dynamic manipulation of nanomechanical resonators in the high-amplitude regime and non-volatile mechanical memory operation * Mahmood Bagheri1 * Menno Poot1 * Mo Li1, 2 * Wolfram P. H. Pernice1 * Hong X. Tang1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:726–732Year published:(2011)DOI:doi:10.1038/nnano.2011.180Received29 July 2011Accepted21 September 2011Published online23 October 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg The ability to control mechanical motion with optical forces has made it possible to cool mechanical resonators to their quantum ground states. The same techniques can also be used to amplify rather than reduce the mechanical motion of such systems. Here, we study nanomechanical resonators that are slightly buckled and therefore have two stable configurations, denoted 'buckled up' and 'buckled down', when they are at rest. The motion of these resonators can be described by a double-well potential with a large central energy barrier between the two stable configurations. We demonstrate the high-amplitude operation of a buckled resonator coupled to an optical cavity by using a highly efficient process to generate enough phonons in the resonator to overcome the energy barrier in the double-well potential. This allows us to observe the first evidence for nanomechanical slow-down and a zero-frequency singularity predicted by theorists. We also demonstrate a non-volatile m! echanical memory element in which bits are written and reset by using optomechanical backaction to direct the relaxation of a resonator in the high-amplitude regime to a specific stable configuration. View full text Subject terms: * NEMS Figures at a glance * Figure 1: The two states of a coupled mechanical resonator–optical cavity system. , Generic optomechanical system (top) in which one of the mirrors in an optical cavity illuminated by a pump laser of frequency ωp and power Pin is able to oscillate at a resonant frequency Ωm. The power circulating inside the cavity, Pcirc, is enhanced by the finesse of the cavity (F = 20). Schematic of the experiment (bottom) showing a nanomechanical resonator embedded in a racetrack-shaped waveguide that serves as the optical cavity (without mirrors). The resonator and waveguide are made of a 110-nm-thick silicon layer. Light is coupled into the bus waveguide via grating couplers (triangles) and then into the cavity. The nanomechanical resonator is made by under-etching a part of the waveguide. The motion of the resonator changes the optical path length (and hence the resonant frequency of the cavity) by changing the effective refractive index of the optical mode. , Scanning electron micrographs of the nanomechanical resonator in its buckled-up (left) and buckled-down ! (right) states. , Optical transmission spectra of the cavity measured at low input power (–5 dBm on coupling bus waveguide) when the resonator is in the up state (blue curve) and the down state (red). The racetrack cavity optical resonances are separated by a free spectral range of 2 nm. , Optical transmission spectrum of the cavity measured at high input power (green, left axis). When the input power exceeds a certain threshold, the spectrum no longer shows the Lorentzian shape seen at low power; rather, the resonance is dragged from the up state to the down state. Moreover, self-sustained oscillations (red, right axis) are observed when ωup < ωp < ωdown, where ωup and ωdown are the resonant frequency of the cavity when the resonator is in the up and down states, respectively. , Thermomechanical noise spectra measured in the up (blue symbols) and down (red) states. Solid black lines are harmonic oscillator responses fitted to the data. * Figure 2: Resolved and unresolved sideband regimes. , Schematic plot of the optical transmission spectrum of the cavity as measured by a weak probe laser of frequency ω when the resonator is at rest (solid green line). The motion of the resonator modifies the effective path length of the optical cavity (Fig. 1a), so that the position of the peak (that is, the resonant frequency of the cavity) changes when the resonator moves (dashed lines). In the high-amplitude regime, the change in the resonance frequency can be larger than the width of the peak. Energy can be exchanged between the laser field and the mechanical motion of the resonator in units of hΩm/2π, where h is Planck's constant and Ωm is the resonator frequency, which leads to optical fields (called sidebands) with frequencies of ωp ± nΩm, where ωp is the frequency of the pump laser and n is an integer. , When the width of the cavity spectrum (green line) is smaller than Ωm, only one sideband can lie inside the cavity linewidth, and this sideband will be ! enhanced by the coupling. In this regime, which is called the resolved sideband regime, only one phonon is exchanged between the optical field and the resonator. , When the width of the cavity spectrum is much larger than Ωm, many sidebands can lie inside the cavity linewidth. In this unresolved sideband regime, more than one phonon can be exchanged between the optical field and the resonator. , Simulations showing the development of self-sustained oscillations over time for a blue-detuned pump laser. The plot at the back shows how the number of photons in the cavity varies with time. The middle plot shows how the resonant wavelength of the cavity varies with time; sometimes it is longer than the wavelength of the pump laser (shown by vertical yellow plane) and sometimes it is shorter. The front plot shows the energy gained (red regions) or lost (blue) by the resonator as a function of time and position. * Figure 3: Optomechanical amplification and relaxation of a nanomechanical resonator in a double-well potential. After the resonator has been excited into a high-amplitude state (left panels) and the pump laser has been turned off, it can relax into the down (middle panels) or up (right panels) states. –, Schematic representation of the amplification and relaxation processes. –, Photodetected voltage versus time, showing an increase in mechanical motion as the pump laser is turned on (), and then a decrease in mechanical motion when the pump laser is turned off (,). –, Fourier spectra of the traces shown in – at different times (indicated by different colours). The wavelength of the probe laser used in panels and differed from that used in the other panels to provide a good transduction in the up state. * Figure 4: Ring-down and zero-frequency singularity. ,, Oscillation frequency () and amplitude () versus time during free decay into the up (blue curve) and down (red) states. The two curves in represent the instantaneous frequency of the resonator obtained from the time traces; the open symbols show the frequency determined from the digital Fourier transform spectra at different times (Fig. 3). The zero-frequency singularity appears as a pronounced dip in the oscillation frequency at 0.02 ms, which coincides with a large change in the oscillation amplitude. , Simulated phase portrait of a resonator relaxing from a high-amplitude state into the up state. The symbols indicate the values at a fixed interval. The parameters used for simulation are extracted from the experiment; however, for clarity, a smaller mechanical quality factor (Qm = 50) was used. * Figure 5: All-optical, non-volatile nanomechanical memory. , Probability of the resonator relaxing to the up state (blue) or down state (red) versus wavelength of the cooling laser (Pin = 7.5 dBm). For certain ranges of wavelengths there is a 100% probability of the resonator relaxing to a given state, so lasers with these wavelengths are used to write data to the nanomechanical memory. An optomechanical instability around 1,560.6 nm is highlighted. , Writing a '1' (left) and a '0' (right) to a nanomechanical memory. First, a reset pulse (blue) excites the resonator to a high-amplitude state. A write pulse of wavelength λ1 (pink, left) or λ0 (red, right) then cools the motion of the resonator into the up state (which represents '1', left) or the down state ('0', right). A weak probe laser (dark blue) then reads the state of the resonator. , Non-volatile memory operation of the resonator. The upper panel shows a series of 10101… written onto the state of the resonator, while in the lower panel a series of 01001…! bits are stored in the memory element. The blue time traces show the series of pulses that reset the memory by exciting large-amplitude oscillations in the resonator. The red (pink) pulses then cool the resonator from the high-amplitude regime into the selected down (up) state; the green time sequence shows the weak probe signal that traces the state of the mechanical resonator. The dark blue shows the state of the memory element. Author information * Abstract * Author information * Supplementary information Affiliations * Department of Electrical Engineering, Yale University, New Haven, Connecticut 06511, USA * Mahmood Bagheri, * Menno Poot, * Mo Li, * Wolfram P. H. Pernice & * Hong X. Tang * Present address: Department of Electrical and Computer Engineering, University of Minnesota, Minnesota 55455, USA * Mo Li Contributions M.B. performed the device fabrication and carried out measurements and data analysis under the supervision of H.X.T. M.B. and M.P. contributed to numerical analysis of the coupled optomechanical system. M.B., M.P., M.L., W.P.H.P. and H.X.T. discussed the results and all authors contributed to the writing of the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Hong X. Tang Author Details * Mahmood Bagheri Search for this author in: * NPG journals * PubMed * Google Scholar * Menno Poot Search for this author in: * NPG journals * PubMed * Google Scholar * Mo Li Search for this author in: * NPG journals * PubMed * Google Scholar * Wolfram P. H. Pernice Search for this author in: * NPG journals * PubMed * Google Scholar * Hong X. Tang Contact Hong X. Tang Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (1,153 KB) Supplementary information Additional data - Unity quantum yield of photogenerated charges and band-like transport in quantum-dot solids
- Nat Nanotechnol 6(11):733-739 (2011)
Nature Nanotechnology | Article Unity quantum yield of photogenerated charges and band-like transport in quantum-dot solids * Elise Talgorn1, 4 * Yunan Gao1, 2, 4 * Michiel Aerts1 * Lucas T. Kunneman1 * Juleon M. Schins1 * T. J. Savenije1 * Marijn A. van Huis2, 3 * Herre S. J. van der Zant2 * Arjan J. Houtepen1 * Laurens D. A. Siebbeles1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:733–739Year published:(2011)DOI:doi:10.1038/nnano.2011.159Received12 July 2011Accepted18 August 2011Published online25 September 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Solid films of colloidal quantum dots show promise in the manufacture of photodetectors and solar cells. These devices require high yields of photogenerated charges and high carrier mobilities, which are difficult to achieve in quantum-dot films owing to a strong electron–hole interaction and quantum confinement. Here, we show that the quantum yield of photogenerated charges in strongly coupled PbSe quantum-dot films is unity over a large temperature range. At high photoexcitation density, a transition takes place from hopping between localized states to band-like transport. These strongly coupled quantum-dot films have electrical properties that approach those of crystalline bulk semiconductors, while retaining the size tunability and cheap processing properties of colloidal quantum dots. View full text Subject terms: * Electronic properties and devices * Nanoparticles * Photonic structures and devices * Synthesis and processing Figures at a glance * Figure 1: Characterization of PbSe QD solids. , Photograph of a PbSe QD solid (brown) on a transparent quartz substrate. The shadow of tree leaves is visible through the smooth and homogeneous film. , Absorption spectra of a QD dispersion and a QD solid. , SEM image at intermediate magnification demonstrating the excellent homogeneity of the film. , High-resolution TEM image. * Figure 2: Ultrafast response of QD solids to optical excitation. , Interband absorption transients of a QD solid at excitation densities Nabs of 0.002 (black curve) to 0.3 (red curve) absorbed photons per QD and probed at the first exciton resonance. , Comparison of interband absorption transients (TA, red curve, left axis) and the real and imaginary terahertz conductivity transients (THz, black and green curves, respectively, right axis) at identical excitation densities of 0.15 absorbed photons per QD. * Figure 3: TRMC photoconductivity of a PbSe QD solid at room temperature. , Incident-fluence-normalized photoconductance transients. The average excitation density, Nabs , is varied from 1 × 10−4 (purple curve) to 7 (red curve) absorbed photons per QD. , ΦmaxΣμ values as a function of the average excitation density for four films prepared using the same procedure. * Figure 4: Temperature dependence of photoconductivity. , ΦmaxΣμ as a function of temperature (90–350 K) and average excitation density (1 × 10−4 to 1 × 102 absorbed photons per QD). The dashed lines are linear fits to the measured data points. , Activation energy as a function of excitation density. Error bars represent standard deviation in the activation energy deduced from the fits in Fig. 3a. * Figure 5: Dependence of the quantum yield of charge carrier photogeneration on temperature in the Onsager–Braun model. The parameters used are as discussed in the text. The rectangle highlights the temperature range where the quantum yield is constant and unity. * Figure 6: Schematic of distribution of electronic states for a QD and its 12 nearest neighbours (as in a close-packed lattice). The smallest energy difference ΔE with one of the neighbours depends on the excitation density, that is, occupation of the levels. For simplicity it is assumed that a QD can host only one electron. Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Elise Talgorn & * Yunan Gao Affiliations * Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands * Elise Talgorn, * Yunan Gao, * Michiel Aerts, * Lucas T. Kunneman, * Juleon M. Schins, * T. J. Savenije, * Arjan J. Houtepen & * Laurens D. A. Siebbeles * Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands * Yunan Gao, * Marijn A. van Huis & * Herre S. J. van der Zant * EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium * Marijn A. van Huis Contributions E.T. and A.J.H. designed the experiment, analysed data and wrote the paper. E.T. performed TRMC experiments. Y.G. and M.A. synthesized the quantum dots and developed the film preparation procedure. Y.G. performed transient absorption measurements and simulations of the mobility. L.K. performed terahertz conductivity experiments. T.J.S. designed the temperature-dependent TRMC setup. J.M.S. developed the analytical deconvolution procedure. M.v.H. performed TEM experiments. H.S.J.v.d.Z. and L.D.A.S. gave conceptual advice. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Arjan J. Houtepen Author Details * Elise Talgorn Search for this author in: * NPG journals * PubMed * Google Scholar * Yunan Gao Search for this author in: * NPG journals * PubMed * Google Scholar * Michiel Aerts Search for this author in: * NPG journals * PubMed * Google Scholar * Lucas T. Kunneman Search for this author in: * NPG journals * PubMed * Google Scholar * Juleon M. Schins Search for this author in: * NPG journals * PubMed * Google Scholar * T. J. Savenije Search for this author in: * NPG journals * PubMed * Google Scholar * Marijn A. van Huis Search for this author in: * NPG journals * PubMed * Google Scholar * Herre S. J. van der Zant Search for this author in: * NPG journals * PubMed * Google Scholar * Arjan J. Houtepen Contact Arjan J. Houtepen Search for this author in: * NPG journals * PubMed * Google Scholar * Laurens D. A. Siebbeles Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (3,140 KB) Supplementary information Additional data - Dynamic internal gradients control and direct electric currents within nanostructured materials
- Nat Nanotechnol 6(11):740-746 (2011)
Nature Nanotechnology | Article Dynamic internal gradients control and direct electric currents within nanostructured materials * Hideyuki Nakanishi1, 2 * David A. Walker1 * Kyle J. M. Bishop3 * Paul J. Wesson1 * Yong Yan1, 2 * Siowling Soh1 * Sumanth Swaminathan4 * Bartosz A. Grzybowski1, 2 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:740–746Year published:(2011)DOI:doi:10.1038/nnano.2011.165Received17 May 2011Accepted06 September 2011Published online16 October 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Switchable nanomaterials—materials that can change their properties and/or function in response to external stimuli—have potential applications in electronics, sensing and catalysis. Previous efforts to develop such materials have predominately used molecular switches that can modulate their properties by means of conformational changes. Here, we show that electrical conductance through films of gold nanoparticles coated with a monolayer of charged ligands can be controlled by dynamic, long-range gradients of both mobile counterions surrounding the nanoparticles and conduction electrons on the nanoparticle cores. The internal gradients and the electric fields they create are easily reconfigurable, and can be set up in such a way that electric currents through the nanoparticles can be modulated, blocked or even deflected so that they only pass through select regions of the material. The nanoion/counterion hybrids combine the properties of electronic conductors with those ! of ionic gels/polymers, are easy to process by solution-casting and, by controlling the internal gradients, can be reconfigured into different electronic elements (current rectifiers, switches and diodes). View full text Subject terms: * Electronic properties and devices * Nanoparticles Figures at a glance * Figure 1: Experimental arrangement. , Scheme of nanoionic gold nanoparticles coated with a monolayer of charged C11NMe3+Cl− thiols. , Nanoparticles used in control experiments were coated with uncharged thiols C11 or C11OH. , Scheme of the nanoionic gold nanoparticle film deposited on a glass substrate. The indicated dimensions are similar for the uncharged nanoparticle films. * Figure 2: Polarization and current rectification in nanoionic nanoparticle films. , Scheme of anion migration and the resulting polarization of the charged nanoparticle film under the influence of an external electric field. , Response in the normalized current density, ≡ j/jmax, of the charged and uncharged nanoparticle films. In this specific example, potential ϕ = 4 V is applied at t = 60 s and is then kept constant. The dotted and dashed lines represent the nanoparticles coated with uncharged thiols C11 and C11OH, respectively. The solid line presents the decay of current density for nanoparticles coated with charged thiols C11NMe3+Cl−. Inset: experimentally measured, normalized current density for C11NMe3+Cl− (solid line) and the exponential fit at long times (dashed line). , Steady-state current densities je as a function of applied potential ϕ for films of nanoparticles functionalized with charged (squares, nonlinear dependence) and uncharged (circles, linear dependence) thiols. The values of je agree with those reported previously for simi! lar nanostructured materials40, 41. , Typical scan of surface potential along the polarized nanoionic film measured by Kelvin force microscopy. , Internal electric potential ϕi induced by application of ϕ = 4 V, where tϕ denotes the time over which the polarizing potential ϕ was applied. The values of ϕi are recorded in an open-circuit configuration in the absence of an external field. The negative sign of ϕi indicates that the direction of the internal field is opposite to that of the initially applied bias. , Scheme of a polarized nanoparticle/C11NMe3+Cl− film and conductance modulation. Application of external field E creates a gradient of counterions within the film and induces internal field Ei (top). When applying another external/probing field E′, the nanoparticle film shows high and low conductance states, depending on the respective directions of E and E′ fields (bottom). , The j–ϕ′ characteristic of the Au/C11NMe3+Cl− nanoparticle film polarized! by applying ϕ = +4 V for 10 min, where ϕ′ is the potentia! l applied during a potential sweep from +4 V to –4 V. Different sweep rates are indicated in the legend. * Figure 3: Current 'steering'. , Optical micrograph of a nanoparticle film located between six electrodes 1–6. Scale bar, 500 µm. , Scheme illustrating polarization of the film, with potential applied between electrodes (5,6) and (2,3). The direction of polarization is indicated by the thick, gradient arrow. Typical polarization times and biases were, respectively, 1–5 s and 4 V. Polarization of the film translates into a higher current along the (1–3) path (thick white arrow) than along the (1–5) path (thin white arrow), I13 > I15. , Plot showing currents along the (1–3) and (1–5) paths (normalized by the maximum current recorded during the experiment, here I13). Horizontal dashed line corresponds to the conductivity of the unpolarized film (same for both paths). Measurements along each path are performed with a bias ϕ = 1.0 V applied sequentially between 1 and 3 and then 1 and 5 electrodes. Each measurement is performed for ~10 s; the time stability of the conductivities along both paths r! eflects the fact that the ionic gradients dissipate over longer timescales (minutes to tens of minutes). ,, Experiments analogous to those in and , but with the direction of the film polarization reversed, that is, from (2,3) towards (5,6). In this case, I15 > I13. * Figure 4: Modelling coupled ion and electron transport. The numerical results illustrated here correspond to the model parameters (neo, nio, De, Di) and are plotted in non-dimensionalized units (Supplementary Section 2.4). , Dimensionless transient current density (solid line) as a function of time following the application of bias = 10. The total electric current includes contributions both from ions (dashed line) and electrons (dotted line). Inset: exponential relaxation of the current towards its steady-state value (see Fig. 2a for the experimental trend). Solid line: experimental; dashed line: fit function. , Dimensionless electric potential across the material as a function of time following the application of a bias of = 10. As ions accumulate at the cathode and are depleted at the anode, spatial variations in the potential become increasingly localized near the electrodes. Even at steady state, however, there remains a finite electric field within the bulk of the material. ,, Distributions of ions and electrons relative to! their equilibrium values as a function of time. Within the bulk of the material, ions and electrons move in concert to maintain local charge neutrality. , Dimensionless steady-state versus characteristic for the nanoparticle material with and without mobile ions. The presence of mobile ions results in non-ohmic behaviour, whereby the ion/electron gradients influence the steady-state electron current. For comparison with experiment, see Fig. 2c. , Current rectification by a polarized ionic nanoparticle material. Initially, the material is completely polarized under a bias of = 10. Subsequent application of different potentials for various times results in the dimensionless current densities shown. The largest current rectification occurs immediately after polarization ( = 0). At longer times, ions and electrons redistribute under the influence of the newly applied bias, gradually erasing the 'memory' of the initial, polarizing bias and decreasing the rectification ratio! . This process is analogous to that shown in Fig. 2g, in which! slower voltage sweeps result in decreased rectification. * Figure 5: Origin of current steering. , Scheme (left) of the polarization of the nanoparticle film and diagram (right) showing qualitative ion distributions (red lines). The mobile ions, represented by red spheres, are few in concentration near electrodes 5 and 6 and high in concentration near electrodes 2 and 3, creating internal electric fields, E15 and E13, as shown. , Scheme (left) of a polarized film in which potential is applied across electrode 1 to electrodes 3 and 5. As shown in the diagram on the right, the internal field along the (1–5) direction 'opposes' the applied field lowering the conductivity of this path; along the (1–3) path, the internal and applied fields are in the same direction, resulting in an increased current (I13 > I15). Additionally, the current along (1–5) is further enhanced relative to that of (1–3) due to the increased concentration of mobile ions. * Figure 6: All-nanoparticle diode. , Configuration of diode consisting of 5.6 nm gold nanoparticles functionalized with positively charged HS–(CH2)11N(Me)3+ thiols and negatively charged HS–(CH2)10COO− thiols (see Supplementary Section 1 for details on device fabrication and dimensions). , Typical j–ϕ curve of the nanoparticle diode device collected with a sweep rate of 0.15 V s−1. , Current profiles for +2 V/−2 V applied voltages switching with a frequency of 5 kHz (red square wave). At this frequency, the steady-state currents measured just before applying the next step function (values indicated by dashed lines, j+ and j−) yield rectification ratios of |j+/j−| ≈ 1.61 ± 0.07. , The rectification ratios increase at longer switching times (for example, ~4.70 ± 0.35 at 125 ms switching time; statistics based on five devices and at least ten measurements for each device). Author information * Abstract * Author information * Supplementary information Affiliations * Department of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA * Hideyuki Nakanishi, * David A. Walker, * Paul J. Wesson, * Yong Yan, * Siowling Soh & * Bartosz A. Grzybowski * Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA * Hideyuki Nakanishi, * Yong Yan & * Bartosz A. Grzybowski * Department of Chemical Engineering, Pennsylvania State University, 132C Fenske Lab, University Park, Pennsylvania 16802, USA * Kyle J. M. Bishop * Department of Materials Science and Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA * Sumanth Swaminathan Contributions H.N. carried out the experiments and data analysis pertaining to TMA nanoparticle films. D.A.W. performed KFM scans, created the figures, edited the text and, with Y.Y., carried out the nanoparticle diode experiments. K.J.M.B. improved upon the preliminary theoretical models by P.J.W., S-L.S. and S.S. by coupling ion and electron migration. B.A.G. conceived the experiments and wrote the paper. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Bartosz A. Grzybowski Author Details * Hideyuki Nakanishi Search for this author in: * NPG journals * PubMed * Google Scholar * David A. Walker Search for this author in: * NPG journals * PubMed * Google Scholar * Kyle J. M. Bishop Search for this author in: * NPG journals * PubMed * Google Scholar * Paul J. Wesson Search for this author in: * NPG journals * PubMed * Google Scholar * Yong Yan Search for this author in: * NPG journals * PubMed * Google Scholar * Siowling Soh Search for this author in: * NPG journals * PubMed * Google Scholar * Sumanth Swaminathan Search for this author in: * NPG journals * PubMed * Google Scholar * Bartosz A. Grzybowski Contact Bartosz A. Grzybowski Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (2,643 KB) Supplementary information Additional data - Nanochannel electroporation delivers precise amounts of biomolecules into living cells
- Nat Nanotechnol 6(11):747-754 (2011)
Nature Nanotechnology | Article Nanochannel electroporation delivers precise amounts of biomolecules into living cells * Pouyan E. Boukany1, 2 * Andrew Morss1, 3 * Wei-ching Liao1, 4 * Brian Henslee1, 2 * HyunChul Jung5 * Xulang Zhang1 * Bo Yu1, 2 * Xinmei Wang1 * Yun Wu1 * Lei Li1 * Keliang Gao1 * Xin Hu1 * Xi Zhao1, 2 * O. Hemminger1, 2 * Wu Lu1, 5 * Gregory P. Lafyatis1, 3 * L. James Lee1, 2 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:747–754Year published:(2011)DOI:doi:10.1038/nnano.2011.164Received03 May 2011Accepted05 September 2011Published online16 October 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * pdf options * download pdf * view interactive pdfpowered by ReadCube * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Many transfection techniques can deliver biomolecules into cells, but the dose cannot be controlled precisely. Delivering well-defined amounts of materials into cells is important for various biological studies and therapeutic applications. Here, we show that nanochannel electroporation can deliver precise amounts of a variety of transfection agents into living cells. The device consists of two microchannels connected by a nanochannel. The cell to be transfected is positioned in one microchannel using optical tweezers, and the transfection agent is located in the second microchannel. Delivering a voltage pulse between the microchannels produces an intense electric field over a very small area on the cell membrane, allowing a precise amount of transfection agent to be electrophoretically driven through the nanochannel, the cell membrane and into the cell cytoplasm, without affecting cell viability. Dose control is achieved by adjusting the duration and number of pulses. The n! anochannel electroporation device is expected to have high-throughput delivery applications. View full text Subject terms: * Nanomedicine * Nanosensors and other devices Figures at a glance * Figure 1: Apparatus and operation of the NEP device. , Top: SEM image of a DNA nanostrand (arrow) 'combed' across two PDMS 'microridges'. Bottom: schematic showing the fabrication of the NEP chip by DCI. , Left: schematic of an NEP chip covered by a PDMS lid with electrodes placed in reservoirs. Middle: optical micrograph of a Jurkat cell in the left microchannel and positioned at the tip of the nanochannel using optical tweezers. The right microchannel contains gene or drugs. Right: SEM image of side view cut of a nanochannel. The nanochannel is ~90 nm in diameter and ~3 µm long. * Figure 2: Comparison of NEP with BEP and MEP. , Left: time dependence of PI dye uptake for NEP (180 V/2 mm, blue curve), BEP (70 V/mm, black) and MEP (150 V/2 mm for 1 µm (red) and 60 V/2 mm for 5 µm (green) cases). All used a single 10 ms pulse. Right: results of the finite-element simulation for the channel, including the maximum electric field (max(E)), the electrophoretic exit velocity and the channel transit time (assuming an electrophoretic mobility of 1 × 10−8 m2 V−1 s−1 for the PI dye). , Fluorescence micrographs of a cell after being transfected with PI dye by NEP, MEP (1 µm case) and BEP. Conditions are as in . The time series of captured images is specified at the bottom of each image. Solid white horizontal lines show the location of micro/nanochannels. The loaded cells in NEP, MEP and BEP devices are specified by dotted circles. The transverse axis was defined by dotted lines to measure the intensity across the cell section (0–1 represents the distance from top to bottom of the cell). , Fluoresc! ence intensity profile along the transverse axis of the cell (shown in ) at different times. * Figure 3: Dosage control by NEP. , Jurkat cells transfected with Cy3-ODN using single 220 V/2 mm pulses of varying durations. Transfection is quantified by the fluorescence signals, which are normalized to the intensity at 60 ms (scale bar, 15 µm). The saturating fluorescence fits a saturating exponential function. , Top: fluorescence micrographs of five cells transfected by NEP chip (scale bar, 60 µm). Bottom: five cells are transfected simultaneously (left) and individually (right) by NEP, showing the repeatability and reliability of the NEP performance. Intensity is expressed in arbitrary units (a.u.). s.d., standard deviation. , Molecular beacon (MB) before hybridization shows dye is quenched (top). After hybridization with target, fluorescence is restored (bottom). , A Jurkat cell transfected (220 V/2 mm) with GAPDH-MB produced fluorescence, but a cell transfected with a scrambled sequence remained dark (scale bar, 15 µm). , Relative MB fluorescence intensities for various pulsing programmes (measur! ed 45 min after NEP). * Figure 4: Critical siRNA dosage to kill cancer cells by NEP. Viability of K562 cancer cells was measured using the LIVE/DEAD assay 18 h after transfection with Mcl-1 siRNA, which downregulates the Mcl-1 protein that inhibits apoptosis. Calcein AM produces green fluorescence in live cells (excitation, 488 nm; emission, 507 nm), and ethidium homodimer (EthD-1) enters cells with damaged membranes and produces red fluorescence in dead cells (excitation, 530 nm; emission, 595 nm). , For NEP pulse durations of 5 ms or longer, sufficient amounts of siRNA entered the cells and the Mcl-1 protein was sufficiently downregulated to induce apoptosis (red dashed box); cells pulsed for 5 ms or less did not receive sufficient amounts of siRNA and therefore remained viable (green dashed box). , All control cells transfected with scrambled siRNA sequence remained alive. , Cell viability under different pulse durations of siRNA (Mcl-1) injection at 220 V/2 mm (pulse length = 1, 2, 3, 4, 5 and 10 ms; number of cells = 8, 9, 7, 7, 8 and 7, respectively). * Figure 5: Theoretical analysis of NEP. , Left: schematic of cell in an NEP device. Right: equivalent electrical circuit of the electroporation system for an intact cell in NEP. , Transport of transfection agents into a cell. The zero of the vertical axis is the entrance of the nanochannel. During the pulse, fringe fields extending into the cell drive molecules through the cell membrane and deep into the cytosol. * Figure 6: Delivery of nanoparticles and plasmids to Jurkat cells. , Quantum dots delivered by BEP, MEP (1 µm) and NEP at 600, 60 and 14 s, respectively, after poration. Location of micro/nanochannels is specified by solid white vertical lines. , Z-stack of confocal microscope images (step size, 1.1 µm) of a cell NEP-porated with 3.5 kbp Cy3-labelled GFP plasmid in a single cell, with the top left image representing the bottom of the cell and the bottom right image the top of the cell. –, Comparison of the delivery of GFP plasmid by BEP (), MEP (5 µm) (60 V/2 mm, two 10 ms pulses) (), NEP (260 V/2 mm, two 5 ms pulses) () and NEP + quantum dots (QDs) after poration (). Fluorescence images: Cy3 (yellow), nucleus (DRAQ-5, blue) and GFP fluorescence (green). BEP was carried out on a NEON transfection system at 1,325 V with three 10 ms pulses for ~1 × 105 cells. See Supplementary Fig. S14 for transfection of pCAG-GFP plasmid (~6.6 kbp) into mouse embryonic fibroblast cells. Author information * Abstract * Author information * Supplementary information Affiliations * Center for Affordable Nanoengineering of Polymeric Biomedical Devices, Ohio State University, Columbus, Ohio 43210, USA * Pouyan E. Boukany, * Andrew Morss, * Wei-ching Liao, * Brian Henslee, * Xulang Zhang, * Bo Yu, * Xinmei Wang, * Yun Wu, * Lei Li, * Keliang Gao, * Xin Hu, * Xi Zhao, * O. Hemminger, * Wu Lu, * Gregory P. Lafyatis & * L. James Lee * Department of Chemical and Biomolecular Engineering, Ohio State University, Columbus, Ohio 43210, USA * Pouyan E. Boukany, * Brian Henslee, * Bo Yu, * Xi Zhao, * O. Hemminger & * L. James Lee * Department of Physics, Ohio State University, Columbus, Ohio 43210, USA * Andrew Morss & * Gregory P. Lafyatis * Department of Mechanical and Aerospace Engineering, Ohio State University, Columbus, Ohio 43210, USA * Wei-ching Liao * Department of Electrical and Computer Engineering, Ohio State University, Columbus, Ohio 43210, USA * HyunChul Jung & * Wu Lu Contributions L.J.L. proposed the concept. P.E.B. and L.J.L. conceived and designed the experiment and analysis. P.E.B. performed the NEP experiments and analysed the data, with contributions from A.M. and G.P.L. regarding the optical tweezers, X. Zhang on cell culture and viability/cytotoxicity, B.Y. on siRNA and molecular beacon NEP, X.W. and Y.W. on cell culture and GFP plasmid NEP and O.H. on DCI. W.L. designed the MEP fabrication process. B.H. and H.J. performed the MEP experiments. W-C.L. and X.H. performed the simulations. L.L., K.G. and X. Zhao performed high-throughput NEP design and experiments. P.E.B., L.J.L. and G.P.L. wrote the manuscript, with input from the other authors. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * L. James Lee Author Details * Pouyan E. Boukany Search for this author in: * NPG journals * PubMed * Google Scholar * Andrew Morss Search for this author in: * NPG journals * PubMed * Google Scholar * Wei-ching Liao Search for this author in: * NPG journals * PubMed * Google Scholar * Brian Henslee Search for this author in: * NPG journals * PubMed * Google Scholar * HyunChul Jung Search for this author in: * NPG journals * PubMed * Google Scholar * Xulang Zhang Search for this author in: * NPG journals * PubMed * Google Scholar * Bo Yu Search for this author in: * NPG journals * PubMed * Google Scholar * Xinmei Wang Search for this author in: * NPG journals * PubMed * Google Scholar * Yun Wu Search for this author in: * NPG journals * PubMed * Google Scholar * Lei Li Search for this author in: * NPG journals * PubMed * Google Scholar * Keliang Gao Search for this author in: * NPG journals * PubMed * Google Scholar * Xin Hu Search for this author in: * NPG journals * PubMed * Google Scholar * Xi Zhao Search for this author in: * NPG journals * PubMed * Google Scholar * O. Hemminger Search for this author in: * NPG journals * PubMed * Google Scholar * Wu Lu Search for this author in: * NPG journals * PubMed * Google Scholar * Gregory P. Lafyatis Search for this author in: * NPG journals * PubMed * Google Scholar * L. James Lee Contact L. James Lee Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (15,108 KB) Supplementary information Movies * Supplementary information (8,421 KB) Supplementary movie 1 * Supplementary information (5,790 KB) Supplementary movie 2 * Supplementary information (537 KB) Supplementary movie 3 * Supplementary information (522 KB) Supplementary movie 4 * Supplementary information (936 KB) Supplementary movie 5 Additional data
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