Diverse Applications

Although there are few sensors today based on pure nanoscience and it is early in the development of nano-enabled sensors, some of the possible devices and applications are already clear. Examples of nanotech and nano-enabled physical, chemical, and biological sensors are given in this section. Although sensors for physical quantities were the focus of early development efforts, nanotechnology will contribute heavily to realizing the potential of chemical and biosensors for safety, medical, and other purposes. Vo-Dinh, Cullum, and Stokes recently provided an overview of nanosensors and biochips for the detection of biomolecules. [12] It is anticipated that many major industries will benefit from nanotechnology-enabled sensors.

Physical Sensors

An early example of a nanotech physical sensor is given in Figure 14-4. Researchers at the Georgia Institute of Technology demonstrated the world's smallest balance by taking advantage of the unique electrical and mechanical properties of carbon nanotubes.[13] They mounted a single particle on the end of a carbon nanotube and applied an electric charge to it. The carbon nanotube acted much like a strong, flexible spring. The nanotube oscillated without breaking, and the mass of the particle was calculated from changes in the resonance vibrational frequency with and without the particle. This approach may lead to a technique for the weight measurement of individual biomolecules.

Figure 14-4. The mass of a carbon sphere shifts the resonance frequency of the carbon nanotube to which it is attached. (Courtesy of Walter de Heer, Georgia Institute of Technology, Atlanta, GA.)

Figure 14-4. The mass of a carbon sphere shifts the resonance frequency of the carbon nanotube to which it is attached. (Courtesy of Walter de Heer, Georgia Institute of Technology, Atlanta, GA.)

Cleland and Roukes at the California Institute of Technology reported the fabrication and characterization of a submicron, mechanical electrometer.M Shown in Figure 14-5, this device, made possible by modern nanofabrication technology, has demonstrated charge sensitivity less than a single electron charge per unit bandwidth (~0.1 electrons/sqrt (Hz) at 2.61MHz). This sensitivity exceeds that of state-of-the-art semiconductor devices.

Figure 14-5. A nanometer-scale mechanical electrometer consists of a torsional mechanical resonator, a detection electrode, and a gate electrode used to couple charge to the mechanical element. (Reprinted with copyright permission from Nature Publishing Group.)

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Figure 14-5. A nanometer-scale mechanical electrometer consists of a torsional mechanical resonator, a detection electrode, and a gate electrode used to couple charge to the mechanical element. (Reprinted with copyright permission from Nature Publishing Group.)

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Chemical Sensors

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