Improved miniature biotelemetric units resembling large pills have been proposed for use in physiological monitoring of the gastrointestinal tract. The broad principles of design, operation, and inexpensive mass production of these sensor pills would be the same as those of the sensor patches described in the preceding article. Of course, the details of design and operation would differ because the patches and pills would be used in different locations and would sense different phenomena.

A Large Pill would contain sensors and electronic circuits for radio telemetry, and perhaps devices for local delivery of drugs. The pill would be interrogated and/or controlled by use of a hand-held radio transceiver. Recent developments in integrated circuits and microelectromechanical system would be exploited in designing and fabricating improved sensor pills.

A sensor pill would be swallowed and would pass through the gastrointestinal tract in about 24 hours. Like the sensor patches described in the preceding article and like some sensor pills now available commercially, a sensor pill of the proposed type would emit a radio signal that would convey its sensor readings to an exterior monitor. Like some other commercially available sensor pills, the proposed sensor pills could include reservoirs of drugs and actuators to deliver the drugs to designated sites.

The proposed pills would incorporate some advances beyond the commercial units. The only sensor readings provided by the commercially available sensor pills are temperature measurements. The proposed sensors would also provide indications of the presence of blood, bacteria, and chemicals of interest. Unlike the commercial sensor pills, the proposed sensor pills would not contain batteries. A sensor pill of the proposed type would be interrogated by use of a hand-held radio transceiver, and would derive its power from a radio beam emitted by the transceiver (see figure), in the same manner as that of a sensor patch described in the preceding article.

The pH sensors would most likely be based on ion-sensitive field-effect transistors (ISFETs), integrated onto the same chips that contain the communication circuits. The temperature sensors could also be integrated onto the same chips.

The bacteria sensors would exploit surface acoustic waves on membranes coated with antigens to the species of interest (for example, H. pylori — the species that causes gastrointestinal ulcers). The bacteria of interest would either attach themselves to the antigens on the membrane or else pull the antigens off; in either case, the result would be a change in the mass of the membrane and thus a change in the acoustic resonance frequency.

Most likely, the sensory areas on a pill would be protected by a cap or by a single-use coat made of a biocompatible polymer, until the time for sensor readings. In preparation for sensor readings, a microelectromechanical actuator could remove a cap; alternatively, a polymer coat could be melted or could be torn off by a microelectromechanical actuator. In the case of an array of sensors, the polymer coat could be removed from any or all sensor(s) at the same time or at different times; thus, even if the sensors were single-use devices, it would be possible to take readings at different times.

This work was done by Gisela Lin, William Tang, and Linda Miller of Caltech and Shlomo Raz of UCLA Medical School for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at  under the Bio-Medical category.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to

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Refer to NPO-20652, volume and number of this NASA Tech Briefs issue, and the page number.

This Brief includes a Technical Support Package (TSP).
Improved sensor pills for physiological monitoring

(reference NPO-20652) is currently available for download from the TSP library.

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

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