LATERAL VISUALIZATION OF DIRECT ELECTRON-TRANSFER BETWEEN MICROPEROXIDASE AND ELECTRODES BY MEANS OF SCANNING ELECTROCHEMICAL MICROSCOPY

Lateral-resolved visualization of direct electron transfer between cys tamine-monolayer modified planar gold electrodes with covalently bound microperoxidase MP-11 is possible using the feedback mode of scanning electrochemical microscopy (SECM). At a potential of the modified gol d electrode of -500 mV versus Ag/AgCl the heme center of microperoxida se can be reduced by means of direct electrochemical communication, an d a suitable redox mediator, which is oxidized at the microtip electro de of the SECM, can subsequently be reduced by the heme. Thus, the red ox reaction of the monolayer-immobilized microperoxidase can be integr ated into the electron-transfer chain between microelectrode and plana r modified gold surface: At free-floating gold electrode potential, th e microperoxidase redox reaction is switched off and a significant blo cking of the immobilization site can be detected. This possibility to switch on and off the direct electron transfer between the gold surfac e and the monolayer-immobilized microperoxidase proves the proposed di rect electron-transfer pathway and allows concomitantly to image immob ilization site and electrochemical properties with a resolution determ ined by the size of the used microtip electrode. (C) 1997 Elsevier Sci ence Limited.