The photoconductivity of carbon nanotubes (CNTs) has been studied theoretically in a nanotube p?n junction, a single SWNT transistor, and thin SWNT films. While individual nanotubes generate discrete fine peaks in optical absorption and emission, macroscopic structures consisting of many CNTs gathered together also demonstrate interesting optical behavior. For example, a millimeter-long bundle of aligned multi-walled nanotubes (MWNTs) emits polarized incandescent light by electrical current heating, and recently researchers in China have made multi-walled nanotubes (SWNT) bundles giving higher brightness emission at lower voltage compared with conventional tungsten filaments. Recent achievements in fabricating self-assembled centimeter-long bundles of CNTs have greatly facilitated study on the macroscopic behavior of these bundle structures. Preliminary results such as an optical polarizer and a light bulb based on CNT macrobundles have been reported.
Researchers have developed a highly sensitive, optical bio-molecule sensor that can distinguish between bio-molecules based on the variation to the light intensity of light due to the change in the path of coupled input light. The variation to the coupled light intensity and path is dependant on the nature of the bio-molecule and the density of the bio-molecules.
Nanoribbons, which are attracting much attention due to their well-defined geometry and perfect crystallinity, require complex and expensive equipment to faricate. Researchers in China have succeeded in fabricating a single nanoribbon sensor and demonstrated its use as a potential in situ monitor to track blood glucose levels, suitable for potential use by diabetics.
The concept of e-noses - electronic devices which mimic the olfactory systems of mammals and insects - is well developed and has become a booming area of research thanks to a better understanding of the reception, signal transduction and odor recognition mechanisms for mammals, combined with achievements in material science, microelectronics and computer science. Researchers have now started replacing the sensing elements in e-noses with nanowires, achieving excellent sensing performance which is comparable or even better compared to the best thin film counterparts.
The oxidation-assisted temperature measurement with carbon nanotube nanothermometers that contain liquid gallium is a novel and reliable method that can be used over a moderate temperature range and can be applied in any environment where air is present. All the other available techniques that are capable to measure temperature at the nanometer scale are limited by either that they are only workable in a very narrow temperature range or that they can only be applied in a special environment.
Nanoscale sensors based on silicon nanowires and carbon nanotubes are capable of detecting molecules at ultra low concentrations. The potential applications include early detection of cancer and fast sequencing of genome. However, for these applications, the time taken by the sensor to reach stable response is crucial. This time is dictated by the diffusion of molecules (e.g. cancer markers) through the solution and their subsequent capture at the sensor surface. Researchers at Purdue University show that this response is governed by the geometry of diffusion of the system and that nanobiosensors are capable of detecting bio-molecules at much lower concentration than the classical planar sensors.
New research shows that ZnO nanostructures are suitable for electrochemical biosensors. The enzyme used for glucose detection, glucose oxidase, was attached to ZnO nanocombs which resulted in a biosensor that exhibits a high affinity, high sensitivity, and fast response for glucose detection. This simple method of fabricating ZnO based biosensor can be extended to immobilize other enzymes and other bioactive molecules on various 1D metal oxide nanostructures, and form versatile electrodes for biosensor studies.
Researchers in Germany report a novel approach for the design of environmental sensors based on fluorescence interference contrast (FLIC) of semiconductor nanocrystals near a reflecting silicon surface. Their method is based on nanocrystals incorporated into polymer layers grafted onto reflecting surfaces.