Fully integrated biocatalytic electrodes based on bioaffinity interactions

Abstract

Integrated bioelectrocatalytically active electrodes are assembled by the deposition of enzymes onto respective electrically contacted affinity matrices and further cross-linking of the enzyme monolayers. A catalyst-NAD +-dyad for the binding of the NAD +-dependent enzymes and cytochrome-like molecules for the binding of the heme-protein-dependent enzymes are used to construct integrated electrically contacted biocatalytic systems. NAD +-dependent lactate dehydrogenase (LDH) is assembled onto a pyrroloquinoline quinone–NAD + monolayer. The redox-active monolayer is organized via covalent attachment of pyrroloquinoline quinone (PQQ) to a cystamine monolayer associated with a Au-electrode, followed by covalent linkage of N 6-(2-aminoethyl)-NAD + to the monolayer. The interface modified with the PQQ-NAD +-dyad provides temporary affinity binding for LDH and allows cross-linking of the enzyme monolayer. The cross-linked LDH is bioelectrocatalytically active towards oxidation of lactate. The bioelectrocatalyzed process involves the PQQ-mediated oxidation of the immobilized NADH. Integrated, electrically contacted bioelectrodes are produced by the affinity binding and further cross-linking of nitrate reductase (NR) (cytochrome-dependent, E.C. 1.9.6.1 from E. coli) or Co II-protoporphyrin IX reconstituted myoglobin (Co II–Mb) atop the microperoxidase-11 (MP-11) monolayer associated with a Au-electrode. The MP-11 monolayer provides an affinity interface for the temporary binding of the enzymes, that allows the cross-linkage of the enzyme molecules. The MP-11 assembly acts as electron transfer mediator for the reduction of the secondary enzyme layer. The integrated bioelectrodes consisting of NR and Co II–Mb show catalytic activities for NO 3 − reduction and acetylenedicarboxylic acid hydrogenation, respectively. Two Fe III-protoporphyrin IX units are reconstituted into a four α-helix bundle de novo protein assembled as a monolayer on a Au-electrode. Vectorial electron transfer proceeds in the synthetic heme-protein monolayer. Cross-linking of an affinity complex generated between the Fe III-protoporphyrin IX reconstituted de novo protein monolayer and NR yields an integrated, electrically contacted enzyme electrode that stimulates the bioelectrocatalyzed reduction of nitrate.