Due to the the increased use of modern bombs in terrorist attacks worldwide, where the amount of metal used is becoming very small, the development of a new approach capable of rapidly and cost-efficiently detecting volatile chemical emission from explosives is highly desirable and urgently necessary nowadays. The trained dogs and physical methods such as gas chromatography coupled to a mass spectrometer, nuclear quadrupole resonance, electron capture detection as well as electrochemical approaches are highly sensitive and selective, but some of these techniques are expensive and others are not easily fielded in a small, low-power package. As a complementary method, however, chemical sensors provide new approaches to the rapid detection of ultra-trace analytes from explosives, and can be easily incorporated into inexpensive and portable microelectronic devices. Researchers in PR China have developed a nanocomposite film that shows very fast fluorescence response to trace vapors of explosives such as TNT, DNT or NB.
Nanoshells are a novel class of optically tunable nanoparticles that consist of alternating dielectric and metal layers. They have been shown to have tunable absorption frequencies that are dependent on the ratio of their inner and outer radii. Therefore nanoshells can potentially be used as contrast agents for multi-label molecular imaging, provided that the shell thicknesses are tuned to specific ratios. When used as contrast agents, nanoshells of small dimensions offer advantages in terms of delivery to target sites in living tissues, bioconjugation, steric hindrance, and binding kinetics. Besides their improved tissue penetration, smaller nanoshells generate a strong surface plasmon resonance and may exhibit absorption peaks in the visible?near-infrared spectrum. Sub-100 nm nanoshells also provide large surface areas to volume ratios for chemical functionalization that can be used to link multiple diagnostic (e.g. radioisotopic or magnetic) and therapeutic (e.g. anticancer) agents. Researchers at Northwestern University have come up with a relatively easy way to synthesize sub-100 nm nanoparticles that give rise to tunable peaks.
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.