Electrochemical-transducer compounds are encapsulated in biocompatible hydrogel structures.

Arrays of electrochemical sensors that include specially coated (as described below) gold electrodes on flexible polyimide sheets have been fabricated and tested in a continuing effort to develop biocompatible, surgically implantable electrochemical-sensor arrays for continuous measurement of concentrations of analytes that play major roles in human and animal metabolism. The effort thus far has been oriented particularly toward developing sensors for monitoring one analyte — glucose — to enable improved treatment of diabetic patients. It is planned to extend this effort to the fabrication and testing of sensors for monitoring lactate and pyruvate and, eventually, to implement the concept of a single array that contains sensors for monitoring glucose, lactate, and pyruvate.

The Prototype Sensor Array shown here contains five individually electrically addressable disk electrodes. In use, only the portion of the strip at the left, containing the five electrodes, would be implanted in the skin of a patient.

Implantable sensors for monitoring glucose have been under investigation for nearly three decades, with mixed and promising results. In the electrochemical- monitoring approach followed in the present development, cyclic voltammetry, amperometry, square-wave voltammetry, or a combination of these techniques is used to measure the rate of catalytic oxidation of glucose by the enzyme glucose oxidase (GOX) in a reaction mediated by poly[vinyl pyridine Os(bipyridine)2Cl] co ethylamine (POs EA), which is an osmium-based polycationic redox polymer. To ensure biocompatibility, the GOX is entrapped in a poly(ethylene glycol) diacrylate (PEG-DA) hydrogel that has previously been demonstrated to be biocompatible.