FORMATION AND IMAGING OF MICROSCOPIC ENZYMATICALLY ACTIVE SPOTS ON ANALKANETHIOLATE-COVERED GOLD ELECTRODE BY SCANNING ELECTROCHEMICAL MICROSCOPY

Microscopic, enzymatically active spots on self-assembled monolayers ( SAMs) of alkanethiolates on gold were obtained by a combination of loc alized desorption induced using the scanning electrochemical microscop e (SECM) followed by chemical derivatization. Starting from a SAM of d odecanethiolate on gold, localized desorption of alkanethiolates creat es microscopic areas of an uncovered gold surface surrounded by a dens e Au alkanethiolate layer. The renewed gold surface chemisorbs an amin o-derivatized disulfide (cystaminium dihydrochloride) in a second step . Periodate-oxidized glucose oxidase was attached covalently to the te rminal amino functions to create a stable, catalytically active patter n of the enzyme on the alkanethiolate SAM. The enzymatic activity was mapped using the imaging capabilities of SECM, The generator-collector mode (amperometric H2O2 detection) was advantageously used, as the fe edback mode leads to interferences due to concurrence between mediator regeneration by the enzymatic reaction and by the heterogeneous elect ron transfer at the gold regions from which the blocking dodecanethiol ate layer had been desorbed. Rising backgrounds due to H2O2 accumulati on in the bulk solution can be prevented by adding minute amounts of t he enzyme catalase to the working solution. By catalyzing the H2O2 dec omposition, the lifetime of H2O2 is adjusted to prevent its accumulati on in the bulk phase yet to allow its diffusion across the gap between the enzyme-modified region and the collecting electrode. Perspectives for creating miniaturized multienzyme structures, which will become a ccessible by repeating the desorption and covalent enzyme immobilizati on steps using different enzymes in each cycle, are highlighted.