Research articles

Polymer–silica nanocomposite gels can be used to culture cells in a three-dimensional environment, offering a way to propagate cells without using enzymes to dissociate them from the surface of conventional cell culture flasks. This approach relies on the dependence of the viscosity of the gel on stress

The first observation of saturating transistor characteristics in a graphene field-effect transistor is reported. The saturation velocity is attributed to scattering by interfacial phonons in the silicon dioxide layer supporting the graphene channels. These results demonstrate the feasibility of graphene devices for analogue and radio-frequency circuit applications without the need for bandgap engineering.

A numerical model of a cell from the electric eel shows that artificial cells can be built to have higher power output densities and greater energy conversion efficiencies than natural cells, allowing them to potentially power medical implants and other devices.

Molecular transport through nanoscale pores is important in many areas of science, but it is difficult to obtain information about the molecules as they pass through the pore. Now it has been shown that imaging with a transmission electron microscope can be used to observe the structure and orientation of a hydrocarbon chain as it passes through a defect in the wall of a carbon nanotube, and also to study how the chain interacts with the nanopore.

Single-electron devices offer many advantages over traditional devices, but it is a challenge to fabricate them in large numbers. A novel geometry in which the source and drain electrodes are vertically separated by thin dielectric films, and nanoparticles attached to the sidewall of the dielectric films act as Coulomb islands, can now be used for the CMOS-compatible fabrication of single-electron devices that operate at room temperature.

The development of molecular devices will require functional molecules that can be integrated into larger architectures and addressed selectively. Now it has been shown that molecular switches, adsorbed in a homogeneous two-dimensional layer, can be collectively switched with spatial selectivity. The probability of a molecule switching is controlled by the surrounding molecules and the supporting surface.

Current techniques to determine reaction rates on the nanoscale measure ensemble averages, making it difficult to relate the catalytic activity of nanoparticles to their morphology. Researchers have now used surface plasmon spectroscopy to observe the kinetics of a redox reaction catalysed by a gold nanoparticle and also the atomic deposition of gold onto a nanocrystal.

The challenge in developing electrical biosensors lies in connecting a molecule detector to an electrical switch. Attaching ion channels to certain cell receptors forms a detector–switch pair that converts chemical information into a measurable electrical signal, creating a platform suitable for screening drugs and other molecules.

Nanoscale particles play an important role in the chemical and biological sciences, but efforts to make nanoparticles from borosilicate glass — which exhibits high tolerance to chemicals and solvents — have proved unsuccessful so far. Now it has been shown that upon mixing a silicon–boron binary oxide solution with water, borosilicate nanoparticles are produced as a result of a vigorous exothermic phase separation.

Conjugated polymer fibres offer many advantages over other photonic materials, such as tunable properties and easy processability, making them attractive for optoelectronic applications. The waveguiding performance and emission tunability of fully conjugated, electrospun polymer nanofibres have been assessed and their forward emission shown to improve after periodic structures are imprinted using nanoimprint lithography.

Semiconducting carbon nanotubes have a direct bandgap, which means that they could form the basis of nanoscale light sources. However, nanotubes tend to emit light over a broad range of wavelengths and directions. Placing the nanotube in a microcavity reduces the spectral width of the output and makes the emission highly directional. This microcavity-controlled, current-driven on-chip emitter is thus an important first step in the development of nanotube-based nanophotonic devices.

Photoacoustic imaging offers higher spatial resolution than most optical imaging techniques, but contrast agents are needed because many diseases in their early stages do not display a natural photoacoustic contrast. Using single-walled carbon nanotubes conjugated with a peptide as a contrast agent allows the non-invasive photoacoustic imaging of tumours in animals.

A combination of quantum dots and fluorescence-interference contrast microscopy can be used to monitor the rotation of microtubules with nanometre accuracy as they glide over motor proteins. This approach shows that the microtubules stop rotating when they pick up large cargos, but their velocity does not change.

The first samples of pristine graphene were obtained by 'peeling off' and epitaxial growth, but chemical approaches are more suited to large-scale production. Exfoliation, reintercalation and expansion of graphite can produce high-quality single-layer graphene sheets suspended in organic solvents, and these sheets can be made into large transparent films by Langmuir–Blodgett assembly.

The performance of state-of-the-art photovoltaic devices based on polymer–nanocrystal composites is still limited by the preparation of the composite films. By blending and annealing cadmium telluride nanocrystals in a polymer–fullerene matrix, high photoconductive gain can be achieved under low applied voltages.

Nanoscale mechanical resonators can make precision measurements of force, position and mass. Atomic resolution in mass sensing at room temperature has now been demonstrated with a carbon nanotube-based resonator that essentially operates as a mass spectrometer. The atomic equivalent of shot noise has also been detected.

The novel electronic properties of graphene can be compromised when it is supported on an insulating substrate. However, suspended graphene samples can display low-temperature mobility values that cannot be attained in semiconductors or non-suspended graphene, and the conductivity approaches ballistic values at liquid-helium temperatures.

Base-pairing drives the assembly of dye-functionalized nanoparticles that have complementary DNA strands attached. This aggregation leads to a massive enhancement of the resonant Raman signal, which may prove useful for sensing applications.

Quantum co-tunnelling through a single-electron transistor limits its performance for many applications. Researchers have now built a nanomechanical single-electron shuttle driven by ultrasound waves in which co-tunnelling is suppressed. This approach could lead to the development of high-performance nanomechanical single-electron devices. (Summary revised 8 July 2008)

Aqueous dispersions of nanoparticles of Triclosan — a commercial antimicrobial agent — display better biocidal activity than organic solutions of the same agent. The nanoparticles are produced by a combination of modified emulsion-templating and freeze-drying.