Hot off the presses! Jul 01 Nat Nanotechnol

The Jul 01 issue of the Nat Nanotechnol is now up on Pubget (About Nat Nanotechnol): if you're at a subscribing institution, just click the link in the latest link at the home page. (Note you'll only be able to get all the PDFs in the issue if your institution subscribes to Pubget.)

Latest Articles Include:

• Of mice and men
  - Nat Nanotechnol 4(7):395 (2009)
  
• Plenty of gloom and doom at the bottom?
  - Nat Nanotechnol 4(7):396-397 (2009)
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• Strictly nanotubes in Beijing
  - Nat Nanotechnol 4(7):398-399 (2009)
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• Our choice from the recent literature
  - Nat Nanotechnol 4(7):400-401 (2009)
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• Top down bottom up: Strength in numbers
  - Nat Nanotechnol 4(7):401 (2009)
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• Nanobiotechnology: A fluid approach to simple circuits
  - Nat Nanotechnol 4(7):403-404 (2009)
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• Nanoelectromechanical systems: Mass spec goes nanomechanical
  - Nat Nanotechnol 4(7):404-405 (2009)
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• Ferroelectric memory: Slim fast
  - Nat Nanotechnol 4(7):405 (2009)
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• Correlated electron systems: Better than average
  - Nat Nanotechnol 4(7):406-407 (2009)
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• Nanomaterials: Sticky but not messy
  - Nat Nanotechnol 4(7):407-408 (2009)
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• Nanotoxicology: How do nanotubes suppress T cells?
  - Nat Nanotechnol 4(7):409-410 (2009)
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• Evaluation of nanoparticle immunotoxicity
  - Nat Nanotechnol 4(7):411-414 (2009)
  The pharmaceutical industry is developing increasing numbers of drugs and diagnostics based on nanoparticles, and evaluating the immune response to these diverse formulations has become a challenge for scientists and regulatory agencies alike. An international panel of scientists and representatives from various agencies and companies reviewed the imitations of current tests at a workshop held at the National Cancer Institute in Frederick, Maryland. This article outlines practical strategies for identifying and controlling interferences in common evaluation methods and the implications for regulation.
• Nanoscale shape-memory alloys for ultrahigh mechanical damping
  - Nat Nanotechnol 4(7):415-419 (2009)
  Shape memory alloys undergo reversible transformations between two distinct phases in response to changes in temperature or applied stress1. The creation and motion of the internal interfaces between these phases during such transformations dissipates energy, making these alloys effective mechanical damping materials2, 3. Although it has been shown that reversible phase transformations can occur in nanoscale volumes4, 5, 6, 7, 8, 9, it is not known whether these transformations have a sample size dependence. Here, we demonstrate that the two phases responsible for shape memory in Cu–Al–Ni alloys are more stable in nanoscale pillars than they are in the bulk. As a result, the pillars show a damping figure of merit that is substantially higher than any previously reported value for a bulk material, making them attractive for damping applications in nanoscale and microscale devices.
• New aspects of the metal–insulator transition in single-domain vanadium dioxide nanobeams
  - Nat Nanotechnol 4(7):420-424 (2009)
  Many strongly correlated electronic materials have a domain structure that greatly influences the bulk properties and obscures the fundamental properties of the homogeneous material. Nanoscale samples, on the other hand, can be smaller than the characteristic domain size, thus making it possible to explore these fundamental properties in detail. Here, we report new aspects of the metal–insulator transition1, 2, 3, studied in single-domain vanadium dioxide nanobeams4, 5, 6. We have observed supercooling of the metallic phase by 50 °C, an activation energy in the insulating phase that is consistent with the optical gap, and a connection between the metal–insulator transition and the equilibrium carrier density in the insulating phase. Our devices also provide a nanomechanical method for determining the transition temperature, enable measurements on individual metal–insulator interphase walls to be made, and allow general investigations of phase transitions in quas! i-one-dimensional geometries.
• Observation of the triplet exciton in EuS-coated single-walled nanotubes
  - Nat Nanotechnol 4(7):425-429 (2009)
  Photon absorption by carbon nanotubes creates bound electron–hole pairs called excitons1, 2, 3, 4, 5, 6, 7, 8, which can exist in spin-polarized triplet or spin-unpolarized singlet configurations. Triplet excitons are optically inactive owing to the weak spin–orbit coupling in nanotubes. This prevents the optical injection of electron spin into nanotubes for spintronic applications9 and limits the efficiency of photocurrent generation10. Here, we show that it is possible to optically excite the triplet exciton by using a ferromagnetic semiconductor as a spin filter11 to mix the singlet and triplet excitons. The triplet contribution to the photocurrent is detected, representing the first direct evidence of the triplet exciton in carbon nanotubes.
• Multifunctional nanoarchitectures from DNA-based ABC monomers
  - Nat Nanotechnol 4(7):430-436 (2009)
  The ability to attach different functional moieties to a molecular building block1, 2 could lead to applications in nanoelectronics3, nanophotonics4, intelligent sensing5 and drug delivery6, 7. The building unit needs to be both multivalent and anisotropic, and although many anisotropic building blocks have been created1, 8, 9, 10, 11, 12, these have not been universally applicable. Recently, DNA has been used to generate various nanostructures13, 14, 15, 16, 17 or hybrid systems18, 19, 20, 21, 22, 23, 24, 25, and as a generic building block for various applications26, 27, 28, 29, 30. Here, we report the creation of anisotropic, branched and crosslinkable building blocks (ABC monomers) from which multifunctional nanoarchitectures have been assembled. In particular, we demonstrate a target-driven polymerization process in which polymers are generated only in the presence of a specific DNA molecule, leading to highly sensitive pathogen detection. Using this monomer syste! m, we have also designed a biocompatible nanovector that delivers both drugs and tracers simultaneously. Our approach provides a general yet versatile route towards the creation of a range of multifunctional nanoarchitectures.
• Droplet networks with incorporated protein diodes show collective properties
  - Nat Nanotechnol 4(7):437-440 (2009)
  Recently, we demonstrated that submicrolitre aqueous droplets submerged in an apolar liquid containing lipid can be tightly connected by means of lipid bilayers1, 2, 3, 4, 5 to form networks4, 5, 6. Droplet interface bilayers have been used for rapid screening of membrane proteins7, 8 and to form asymmetric bilayers with which to examine the fundamental properties of channels and pores9. Networks, meanwhile, have been used to form microscale batteries and to detect light4. Here, we develop an engineered protein pore with diode-like properties that can be incorporated into droplet interface bilayers in droplet networks to form devices with electrical properties including those of a current limiter, a half-wave rectifier and a full-wave rectifier. The droplet approach, which uses unsophisticated components (oil, lipid, salt water and a simple pore), can therefore be used to create multidroplet networks with collective properties that cannot be produced by droplet pairs.
• Transfer of gold nanoparticles from the water column to the estuarine food web
  - Nat Nanotechnol 4(7):441-444 (2009)
  Within the next five years the manufacture of large quantities of nanomaterials may lead to unintended contamination of terrestrial and aquatic ecosystems1. The unique physical, chemical and electronic properties of nanomaterials allow new modes of interaction with environmental systems that can have unexpected impacts2, 3. Here, we show that gold nanorods can readily pass from the water column to the marine food web in three laboratory-constructed estuarine mesocosms containing sea water, sediment, sea grass, microbes, biofilms, snails, clams, shrimp and fish. A single dose of gold nanorods (65 nm length 15 nm diameter) was added to each mesocosm and their distribution in the aqueous and sediment phases monitored over 12 days. Nanorods partitioned between biofilms, sediments, plants, animals and sea water with a recovery of 84.4%. Clams and biofilms accumulated the most nanoparticles on a per mass basis, suggesting that gold nanorods can readily pass from the water c! olumn to the marine food web.
• Towards single-molecule nanomechanical mass spectrometry
  - Nat Nanotechnol 4(7):445-450 (2009)
  Mass spectrometry provides rapid and quantitative identification of protein species with relatively low sample consumption. The trend towards biological analysis at increasingly smaller scales, ultimately down to the volume of an individual cell, continues, and mass spectrometry with a sensitivity of a few to single molecules will be necessary. Nanoelectromechanical systems provide unparalleled mass sensitivity, which is now sufficient for the detection of individual molecular species in real time. Here, we report the first demonstration of mass spectrometry based on single biological molecule detection with a nanoelectromechanical system. In our nanoelectromechanical–mass spectrometry system, nanoparticles and protein species are introduced by electrospray injection from the fluid phase in ambient conditions into vacuum, and are subsequently delivered to the nanoelectromechanical system detector by hexapole ion optics. Precipitous frequency shifts, proportional to t! he mass, are recorded in real time as analytes adsorb, one by one, onto a phase-locked, ultrahigh-frequency nanoelectromechanical resonator. These first nanoelectromechanical system–mass spectrometry spectra, obtained with modest mass sensitivity from only several hundred mass adsorption events, presage the future capabilities of this approach. We also outline the substantial improvements that are feasible in the near term, some of which are unique to nanoelectromechanical system based-mass spectrometry.
• Mechanisms for how inhaled multiwalled carbon nanotubes suppress systemic immune function in mice
  - Nat Nanotechnol 4(7):451-456 (2009)
  The potential health effects of inhaling carbon nanotubes are important because of possible exposures in occupational settings. Previously, we have shown mice that have inhaled multiwalled carbon nanotubes have suppressed systemic immune function. Here, we show the mechanisms for this immune suppression. Mice were exposed to 0, 0.3 or 1 mg m-3 multiwalled carbon nanotubes for 6 h per day for 14 consecutive days in whole-body inhalation chambers. Only those exposed to a dose of 1 mg m-3 presented suppressed immune function; this involved activation of cyclooxygenase enzymes in the spleen in response to a signal from the lungs. Spleen cells from exposed animals partially recovered their immune function when treated with ibuprofen, a drug that blocks the formation of cyclooxygenase enzymes. Knockout mice without cyclooxygenase enzymes were not affected when exposed to multiwalled carbon nanotubes, further confirming the importance of this enzyme in suppression. Proteins f! rom the lungs of exposed mice suppressed the immune function of spleen cells from normal mice, but not those from knockout mice. Our findings suggest that signals from the lung can activate signals in the spleen to suppress the immune function of exposed mice.
• Self-assembled cationic peptide nanoparticles as an efficient antimicrobial agent
  - Nat Nanotechnol 4(7):457-463 (2009)
  Antimicrobial cationic peptides are of interest because they can combat multi-drug-resistant microbes. Most peptides form -helices or -sheet-like structures that can insert into and subsequently disintegrate negatively charged bacterial cell surfaces. Here, we show that a novel class of core–shell nanoparticles formed by self-assembly of an amphiphilic peptide have strong antimicrobial properties against a range of bacteria, yeasts and fungi. The nanoparticles show a high therapeutic index against Staphylococcus aureus infection in mice and are more potent than their unassembled peptide counterparts. Using Staphylococcus aureus-infected meningitis rabbits, we show that the nanoparticles can cross the blood–brain barrier and suppress bacterial growth in infected brains. Taken together, these nanoparticles are promising antimicrobial agents that can be used to treat brain infections and other infectious diseases.