Direct electrochemistry with nitrate reductase in chitosan films

Stable films made from chitosan (CS) on pyrolytic graphite (PG) electrode gave direct electrochemistry for incorporated enzyme nitrate reductase (NR). Cyclic voltammetry (CV) of NR-CS films showed a pair of well-defined and nearly reversible redox peaks at about -0.430 V vs. SCE at pH 7.0 phosphate buffers, which was considered as the redox of FAD and heme-ion. The electron transfer between NR and PG electrode was greatly facilitated in CS films. Integration of reduction peaks at different scan rates from 0.01 to 0.5 V s^-1 gave nearly constant charge values, which is characteristic of thin-larger- electrochemical behavior. The pH of the solution strongly affected the direct electron transfer of NR-CS films. EDTA accelerated the electron transfer, and it was proposed as a stimulant for the system. Reflectance absorption infrared spectra demonstrated that NR retained a nearly native conformation in CS films.