A pyruvate oxidase electrode based on an electrochemically deposited redoxpolymer

A. redox polymer-modified, multilayer biosensor for the determination of py ruvate and phosphate in oxygen-free samples has been developed. The new, hi ghly conductive redox polymer was produced by potentiostatic copolymerizati on (+1.4V vs. Ag/AgCl) of Os(bipy)(2)pyCl-modified pyrrole monomer (6 x 10( -3) mol L-1) and thiophene (1 x 10(-3) mol L-1) on top of a platinized glas sy-carbon electrode. The redox polymer-coated platinum black layer with inc reased active surface area permitted the adsorption of pyruvate oxidase as the biological recognition element and efficient electron transfer from enz yme-bound FAD-groups to the electrode. Pyruvate was detected at anodic pote ntials (350-500 mV) in oxygen-foe solution in the presence of phosphate as the cosubstrate with a linear range from 0.02 x 10(-3) to 0.3 X 10(-3) mol L-1. A sensitivity as high as 0.2 A cm(-2) mol(-1) L was obtained. Phosphat e was measured similarly between 0.02 x 10(-3) and 0.5 x 10(-3) mol L-1 in the presence of pyruvate as co-substrate. The sensitivity of the sensor dro pped to about 12 % after 10 days. Since interference by ascorbate, due to t he high formal potential of the used Os(bipy)(2)pyCl-group, could be a prob lem in real samples, coverage of the adsorbed enzyme by a polycationic size exclusion layer of polypyrrole was investigated. Compared to former enzyme electrodes utilizing pyruvate oxidase, the new approach offered an unprece dentedly high sensitivity, O-2- and thiamindiphosphate-independent operatio n and presented a large step towards electrochemical pyruvate determination in vivo.