As their name suggests, nerve agents attack the nervous system of the human body. All such agents function the same way: by interrupting the breakdown of the neurotransmitters that signal muscles to contract, preventing them from relaxing. Nerve agents, depending on their purity, are clear and colorless or slightly colored liquids and may have no odor or a faint, sweetish smell. They evaporate at various rates and are denser than air, so they accumulate in low areas. Nerve agents include tabun(GA), sarin(GB), soman(GD), and VX. The military has a number of devices to detect nerve agent vapor and liquid. Current methods to detect nerve agents include surface acoustic wave (SAW) sensors, conducting polymer arrays, vector machines, and the most simple, color change paper sensors. Most of these systems have have certain limitations including low sensitivity and slow response times. By using readily synthesized network films of single-walled carbon nanotube bundles researchers have built a sensor capable of detecting G-series nerve agents such as Soman and Sarin (Sarin was used in the Tokyo subway terrorist attack in 1995). This research opens new opportunities in the design of real-time chemical warfare agent (CWA) sensors with independent response signatures.
The ability to detect few or individual molecules in solution is at present largely limited to fluorescence techniques, and a comparable method using electrical detection has so far remained elusive. Such a technique would be highly desirable for lab-on-a-chip applications and when labeling with fluorophores is invasive or impossible. More importantly, it would pave the way for fluidic devices in which individual ions are electrically detected and manipulated, allowing a new class of fundamental experiments on nonequilibrium statistical physics, transport at the molecular scale, and a broad range of biophysical systems. Researchers in The Netherlands now have demonstrated a new nanofluidic device for the detection of electrochemical active molecules with an extremely high sensitivity. A prototype device allows detecting fluctuations due to Brownian motion of as few as approx. 70 molecules, a level heretofore unachieved in electrochemical sensors. Ultimately, the researchers hope the device will not only be able to detect single molecules in the device, but also discriminate between various species.
As the most common endocrine metabolic disorder for human beings, diabetes mellitus with an obvious phenomenon of high blood glucose concentrations results from a lack of insulin. Despite the availability of treatment, diabetes has remained a major cause of death and serious vascular and neuropathy diseases. Continuously monitoring the blood glucose level and intermittent injections of insulin are widely used for effective control and management of diabetes. Extensive research has been conducted to develop optimal glucose sensors for diagnostic purposes. Currently, the commercially available glucose biosensors still have some problems to overcome, such as time consuming, relatively low sensitivity, bad reliability. The performance of a glucose sensor is largely dependent upon the materials which construct the sensor. Recent research effort for glucose sensing have turned to on nanomaterials. Nanomaterial-based biosensors already have shown the capability of detecting trace amounts of biomolecules in real time. New research has studied the electrochemical characteristics of platinum decorated carbon nanotubes (CNTs) as a promising candidate for glucose sensing. Its improved performance may encourage further exploration of this novel nanomaterial in the field of bioapplications.
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.