A novel amperometric transducer design for needle-type implantable biosensor applications

A novel transducer design is proposed based on a electrocatalyst for hydrogen peroxide oxidation (platinum black) electrodeposited on the inner wall of a stainless steel needle which serves as a working electrode, and an external Ag/AgCl reference/counter electrode. Electropolymerized 1,3-diaminobenezene (1,3-phenylenediamine) is employed as a protective layer for the platinum black as well as an interference eliminating layer. This configuration uses the Pt electrocatalyst in its most active dispersed form and ensures good mechanical ruggedness and protection of the catalytic and biological components. The design also provides the possibility to obtain high enzyme loading and hence an extended sensor life-time. Two types of glucose sensors were constructed based on this novel design concept. The enzyme (glucose oxidase) was immobilized either in a hydrophilic gel matrix inside the needle body (i) or cross-linked on the inner needle surface (ii). Cellulose triacetate, polycarbonate, and Nafion were used as external diffusion control layers, which extended the linear range of the sensor response to over 25 mM glucose. These biosensors demonstrated diminished response to interferences from oxidizable compounds present in body fluids and a life time of at least three months.