Nanosensors have been developed for chemical detection using carbon nanotubes (CNTs). Unlike other chemical sensors, this solid-state approach requires no reagents and can be refreshed with a solid-state ultraviolet (UV) diode. The sensors possess high sensitivity (ppbv), fast response (≈2 s), high selectivity, low power (μW), and very small size (1 cm2 or less based on advanced miniaturization), and they are ideally suited for integration with wireless networks or cellphone type devices.
Selectivity is provided by integrating multiple sensors on a single chip, and modifying CNTs or nanowires on each sensor with different functional groups, polymer coatings, and/or dopants of metal catalytic nanoparticles. All sensors use simple absorbate-modulated-resistance (I/V) measurements combined with pattern-recognition software for identifying gases and their concentrations. The detectors are fast, have a high probability of detection (PD), high selectivity, and very low false alarm rate (FAR).
The sensors work well as radiation detectors for protons and gamma rays, and can detect the chemicals and radiation simultaneously. The sensors have been demonstrated for surveillance (chemical “sniffers”), as well as quick screening for hazardous materials. Unlike most other detection technologies, the sensors have demonstrated in-situ and real-time detection without moving the sample offline in order to distinguish hazardous materials from innocuous items such as water, wine, or suntan lotion.
The invention is an electronic nose sensor, about the size of a postage stamp, that includes an array of nanosensors and associated signal processor to estimate which chemicals are present and the concentrations of those that are present. This information is then transmitted, using the cellphone, to a network that delivers this information to a chemical reporting module. Thus far, the chemicals that can be sensed (down to about 10 ppb concentrations) include H2O2, NO2, NH3, Cl2, HCN, N2H4, CH4, benzene, acetone, formaldehyde, dinitrotoluene, and some chemical warfare agents. Sensor response time for a given chemical ranges from 2 s (for H2O2 detection) to several tens of seconds for some difficult substances. A 32- or 64-channel nanosensor is utilized to perform multiple track testing to monitor for several chemicals, using changes in resistance or in another indicium.