Letters in 2008

Colloidal semiconductor nanocrystals are widely used in biological imaging, but existing synthesis techniques are difficult and require specialized expertise. Here it is shown that the use of DNA as a ligand allows a simpler synthetic protocol to be used, producing biofunctionalized nanocrystals that exhibit strong optical emission in the visible spectrum, minimal toxicity and small hydrodynamic diameter.

The production of functional molecular architectures through self-assembly is commonplace in nature, but it is still a major challenge to achieve similar complexity in the laboratory. It has now been shown that reversible enzyme-catalysed reactions can drive synthetic self-assembly. This approach could ultimately lead to the fabrication of functional nanostructures with enhanced complexities and fewer defects.

The electrical conductance of a nanotube decreases when it is heated. This phenomenon is exploited in a new technique called photothermal current microscopy to image the conductance of individual nanotubes and groups of nanotubes.

The photoluminescence properties of carbon nanotubes are sensitive to molecular adsorption. By studying the response of a pair of single-wall carbon nanotubes, researchers have now shown that analytes of biological interest can be identified and measured in real-time within living cells.

Research suggests that citizens use 'religious filters' as an important cognitive shortcut for many scientific issues, including nanotechnology. Combining the results of surveys in the United States and Europe, it has been found that US respondents were significantly less likely to agree that nanotechnology is morally acceptable than respondents in many European countries. These moral views correlated directly with aggregate levels of religiosity in each country.

Most techniques for producing graphene use graphite as a starting material and are labour-intensive. The direct chemical synthesis of carbon nanosheets in gram-scale quantities from the common laboratory reagents ethanol and sodium has now been demonstrated. The ability to produce bulk graphene samples from non-graphitic precursors with a scalable, low-cost approach should take us a step closer to real-world applications of graphene.

Public surveys provide valuable information on how people view nanotechnology, but cannot easily uncover more detailed responses to the complexities of any new technology. Four concurrent workshops debating energy and health nanotechnologies in the US and UK found that energy applications were viewed more positively than those for health in both countries.

A sample of 1,862 adults was presented with balanced information on the risks and benefits of nanotechnology. Subjects did not react in a uniform manner, but polarized along lines consistent with cultural predispositions towards technological risk generally.

The mechanical deposition of single molecules on a surface can be optically monitored with nanometre precision using a combination of total internal reflection fluorescence microscopy and atomic force microscopy.

Nanogenerators based on piezoelectric nanowires have already been demonstrated, but these devices were not mechanically robust. A new approach overcomes such problems by avoiding sliding contacts. Repeatedly stretching and releasing a piezoelectric wire in the new devices can generate electricity with an efficiency of 6.8%.

Previous photodetectors based on solution-processed colloidal quantum dots have demonstrated either rapid response times or high sensitivity. Researchers have now taken advantage of new insights into charge transport in these devices to build photodiodes that offer both rapid response times and high sensitivity.

Graphene is a promising material for the next-generation of nanoelectronic devices, but it has been difficult to produce single-layer samples in bulk quantities. A solution-based process for the large-scale production of single-layer, chemically converted graphene has now been demonstrated and used to make field-effect devices with currents that are three orders of magnitude higher than previously reported for chemically produced graphene.

Carbon nanotubes used as templates for polymerizing lipids into regular ring-shaped water-soluble assemblies that can dissolve various hydrophobic compounds and membrane proteins, could have applications in cosmetics, medicine and materials science.

When a spin-polarized current passes from a ferromagnet into a non-magnetic material, the spins of the itinerant electrons are ‘flipped’ at the interface between the two materials, producing a mechanical torque. A nanoscale torsion oscillator has now measured this torque in a metallic nanowire in which one half is ferromagnetic and the other non-magnetic. The unprecedented torque sensitivity offered by this device could have applications in spintronics and fundamental physics, chemistry and biology.

Most experiments on nanoelectromechanical systems (NEMS) have so far been performed in the frequency domain, whereas applications in computation and information storage will require such systems to be operated in the time domain. A time-resolved optical approach to the transduction of ultrahigh-frequency NEMS that works at frequencies from less than 10 MHz to over 1 GHz has now been demonstrated.

Fibre lasers are used as light sources in many fields of science and technology, and the inclusion of a saturable absorber inside the laser cavity enables ultrafast pulses to be generated. It has now been demonstrated that single-wall carbon nonotubes are excellent saturable absorbers, especially in the 1.3–1.5 μm wavelength region used for optical communications, enabling the output of ultrafast fibre lasers to be tuned over wide range of wavelengths.

Local heating and conduction will have a major role in the stability of nanoscale devices based on molecular junctions, so reliable methods are needed to measure the temperature of such junctions. Researchers have now developed a technique to monitor the effective temperature of current-carrying molecular junctions based on surface-enhanced Raman spectroscopy.

Most solids expand when they are heated, but some non-magnetic materials expand when they are cooled. Researchers have now observed evidence for negative thermal expansion (NTE) in nanocrystals of two magnetic materials. Moreover, the NTE effect in nanocrystals of CuO is four times larger than that observed in the celebrated NTE material zirconium tungstate.

Maskless nanolithography is a flexible nanofabrication technique but it suffers from low throughput. By developing a new approach that involves 'flying' an array of plasmonic lenses just 20 nm above a rotating surface, it is possible to increase throughput by several orders of magnitude.

Confining light below the diffraction limit is likely to be a feature of future optical data transmission systems, but it will be necessary to integrate such waveguides with diffraction-limited components. The coupling of light from a polymer optical waveguide into multiple silver nanowire plasmonic waveguides shows that this will be possible.