H2O2-GENERATING PEROXIDASE ELECTRODES AS REAGENTLESS CYANIDE SENSORS

Inexpensive, reagentless, and simple (single-electrode) cyanide biosen sors are developed using a pyrolytic graphite (PG) electrode on which horseradish peroxidase (HRP) is adsorbed. The electrode is poised at - 300 mV vs Ag/AgCl for 40 s to reduce dissolved O-2 to H2O2 at the PG s urface. The generated H2O2 accumulates in the diffusion layer. The pot ential is then stepped to 0 mV, at which the accumulated H2O2 is reduc ed, though the O-2 reduction does not proceed. Since the H2O2 reductio n is catalyzed by HRP, the transient cathodic current is inhibited by cyanide. Therefore, the transient current is a function of the cyanide concentration. A HRP/PG electrode with saturated HRP coverage is reli able, and it can determine 10(-5)-10(-3) M cyanide. On the other hand, the electrode with lower HRP coverage is less reliable, though it is so sensitive as to detect 2 x 10(-7) M cyanide because the system is u nder kinetic control.