Characterization of the direct electron transfer and bioelectrocatalysis of horseradish peroxidase in DNA film at pyrolytic graphite electrode

Direct electron transfer between horseradish peroxidase (HRP) in a DNA film and pyrolytic graphite (PG) electrode was observed at the formal potential of -0.208 V (versus Ag/AgCl (sat. KCI)) involving the Fe-III/Fe-II redox c ouple. DNA played the role of charge carrier and facilitated the electron t ransfer between HRP and the PG electrode. The peak current of the redox pro cess increased linearly with scan rate from 0.05 to 2 V/s, which is typical in thin layer electrochemistry. The number of electrons and the average ap parent heterogeneous electron transfer rate constant k(s) involved in the r edox reaction were calculated to be 0.94 and 1.130 s(-1), respectively. The formal potential dependence on pH with 54 mV per pH indicated a one-proton -transfer coupled with a one-electron-transfer reaction. Scanning electron microscopy (SEM) showed the different morphologies for isolated DNA film an d the complex film of HRP and DNA. Visible absorption and reflectance-absor ption infrared (RAIR) spectra proved the heme environment of HRP in DNA fil m to be in its native status. The embedded HRP molecules in DNA him retaine d the electrocatalytic activity for hydrogen peroxide. The sensitivity of t he HRP-DNA-PG biocomposite was 115.6 mu A/cm(2) for 2.5 x 10(-4) mol/l H2O2 . This HRP-DNA film modified PG electrode represented a valid example of me diator-free amperometric biosensors. (C) 2000 Elsevier Science B.V. All rig hts reserved.