Electrobiotic sensors have been proposed for detecting toxic substances in a variety of environments. Electrobiotic sensors would be inexpensive, compact units that would be easy to use and could be deployed either singly or in large numbers, depending on the size of an environment to be monitored and/or the need to locate a toxic source within a larger area. For example, multiple electrobiotic sensors might be deployed on a battlefield or at a large-scale mining operation, whereas a single electrobiotic sensor might be used to monitor the air in a laboratory or at an assembly bench where toxic chemicals are used.

An Electrobiotic Toxic-Agent Sensor would contain and monitor a population of small nematodes. Electronic circuitry would detect motion or lack of motion of the nematodes. Upon detecting cessation of the motion (presumably a result of environmental toxicity), the circuitry would transmit a signal. The total volume of the sensor would be about 1 in.3 (16 cm3).
The term "electrobiotic" was chosen for these sensors because the front line of sensitivity would be biological entities and the responses of these entities to toxic substances would be sensed and processed by electronic circuitry. More specifically, a typical electrobiotic sensor (see figure) would include very small live nematodes in a suitable medium deposited on an active-pixel sensor (APS) [a state-of-the art single-chip integrated-circuit array of photodetectors and active readout circuitry]. The movements of the nematodes, which are mutatable to be agent-specific, would be detected through differencing between prompt and delayed pixel readout signals.

A control application-specific integrated circuit (ASIC) on a single chip would monitor the pixel-differencing output of the APS chip to detect movement. If movement were detected, no further action would be taken. If movement were not detected, the control ASIC would activate a microfluidic injection of nicotine to stimulate activity of the nematodes. If activity were still not detected, the nematodes would be assumed to be dead, implicating a toxic environment. The ASIC would then activate the radio transmission of a simple binary signal containing encrypted data on the location of the sensor as determined by a Global Positioning System (GPS) receiver that would also be part of the sensor. If multiple electrobiotic sensors were dispersed over a large area, then they could communicate with each other to relay their status and location data to a central receiver/repeater unit, which would be placed in the area during dispersal of the sensors.

The radio transmitter in an electrobiotic sensor could be very simple and short-lived and its range could be limited [e.g., of the order of a mile ( ≈ 1.6 km)]. Therefore, the power demand of the sensor could be satisfied with a very small battery like that used in a hearing aid.

The life cycles of nematodes are typically of the order of 4 days. However, nematodes can be sustained in a dormant state for a few weeks to a few months. Furthermore, they can be frozen for very long periods. Hence, electrobiotic sensors could be stored at low temperatures for future use.

This work was done by Philip Moynihan, Robert Stirbl, and Roger Kern of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP)free on-line at www.nasatech.com/tsp  under the Electronics & Computers category. NPO-20721

This Brief includes a Technical Support Package (TSP).
Electrobiotic Toxic-Agent Sensors

(reference NPO-20721) is currently available for download from the TSP library.

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This article first appeared in the May, 2000 issue of NASA Tech Briefs Magazine.

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