Nanotechnology holds promise for security applications

How state-of the-art sensor technology could be used for detecting and combating chemical, biological agents

The world today is seemingly filled with multiple threats from every direction and of every type;   physical damage caused by fire or water, natural events like seismic activity or floods, disruption of essential services like electricity or communication, and compromise or loss of information.  In most cases, it is obvious that damage has been done. Computers may no longer be operative,   physical structures may be destroyed and communication systems may not work.  However, in the case of the more insidious harm that may be caused by chemical, biochemical, radiological or disease-causing agents, it may be some time before overt effects can be detected. 

In order to be able to take appropriate reparative or preventative countermeasures, it is imperative to be able to discover a threat as soon as possible.  However, traditional methods for detecting chemical and biological agents are often slow and require skilled labor.  If we are to minimize the effects of a hostile intentional action, detection instruments must not only be accurate, highly specific, compact, operational for long periods of time, and capable of being easily deployed, but they also must be able to detect substances that were not traditionally a concern.  These include the gaseous chemical signals emitted by pathogens, diseases, pesticides, toxins and explosives.  Without an appropriate surveillance program it is likely that the first indication that an attack has occurred will be when multitudes of people show up for treatment in hospital emergency departments. 

Sensor technology, especially using engineering developments centering on nanotechnology, hold great promise for the early detection of disease.  Indeed, we are now at the point with nanosensor technology that individual molecules can be identified.  Researchers at the Fresnel Institute in Marseille, France, have created an optical device the size of a large protein molecule that detects biological molecules using fluorescence brightness in sample sizes stated to have the smallest observation volume in the world.  This technology could be incorporated into instruments used for early diagnosis of disease markers.

For several years now, it has been recognized that nanostructures, such as nanotubes and nanowires (some of the functional building blocks of nanotechnology ranging from 1 to 100 nanometers in size) and sheets and ribbons of graphene (a two-dimension sheet of carbon atoms arranged in a lattice) have the ability to sense gases due to their very high surface-to-volume ratio and surface adsorption.  The latter is the same phenomenon by which activated charcoal in a gas mask attracts toxic gas molecules and allows the person wearing the mask to breathe uncontaminated air.  Altering both the chemical composition of the surface and the shape of the underlying nanostructure allow different gases to be adsorbed.  When these gas molecules adhere to the surface, the electrical properties of the substrate change and permit measurement of both the type and concentration of the gas.

Using these techniques, an “electronic nose” is under development by Professor Nosang Myung at the University of California, Riverside.  This device uses an array of carbon nanotubes to detect airborne toxic substances at a level of parts per billion.  It is anticipated that the sensor would be used for detecting chemical warfare agents, gas leaks, volatile organic compounds and toxic pesticides.  The early prototype model was reported to be about four by seven inches in diameter. The goal is to reduce that to the size of a credit card and, ultimately, the size of a fingernail so that it could be incorporated into a variety of platforms, including smartphones, handheld devices and wearable formats.  The human skin is known to produce volatile organic compounds that are associated with diseases that include cancers, genetic disorders and viral and bacterial infections. This sensing technology could also be used for disease detection as well.

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