Interface Electronic Circuitry for an Electronic Tongue

Compact, low-noise interface circuits are mounted in proximity to the tongue.

Electronic circuitry has been developed to serve as an interface between an electronic tongue and digital input/output boards in a laptop computer that is used to control the tongue and process its readings. Electronic tongues were described in two prior NASA Tech Briefs articles: “Electronic Tongue for Quantitation of Contaminants in Water” (npo-30601), Vol. 28, No. 2 (February 2004), page 31; and “Electronic Tongue Containing Redox and Conductivity Sensors” (NPO- 30862), Vol. 31, No. 8 (August 2007), page 58. Electronic tongues can be used for a variety of purposes, including evaluating water quality, analyzing biochemicals, analyzing biofilms, and measuring electrical conductivities of soils.

The present electronic tongue and interface circuitry are updated versions of those described in the latter-mentioned prior article. The instrument was designed for use in characterizing biofilms by Prof. D. Newman and Dr. D. Lies at Caltech. To recapitulate: An electronic tongue is a rugged, compact sensor unit that can include a heater, a temperature sensor, a conductivity sensor, and an array of three-electrode electrochemical cells, all on one planar surface of a ceramic substrate. The cells of an electronic tongue are connected to electronic excitation and readout circuits. Among the tasks identified by Prof. D. Newman and Dr. D. Lies that must be performed to characterize biofilms are stimulation of the microbial environment through generation of oxygen and hydrogen, detection of their metabolic products, and visual observation of biofilms. An electronic tongue can provide the needed stimulation while serving as a means of electrochemical detection of metabolic products of a biofilm.

A prototype apparatus for characterizing a biofilm includes an electronic tongue mounted in a flow-through, seeinto chamber. The chamber is mounted on a platform under a microscope that is used to observe the biofilm growing on the electronic tongue. The flowthrough, see-into chamber is made of polycarbonate structural components plus a cover glass. A watertight compartment containing the electrodes is formed by O-ring seals between the upper and lower surfaces of the electronic tongue and the facing surfaces of the chamber. On the top side of the electronic tongue, a spacer establishes the thickness of the flow-through cell as a gap between the electrodes and the cover glass.