Assembly of functionalized monolayers of redox proteins on electrode surfaces: Novel bioelectronic and optobioelectronic systems

Functionalized monolayer electrodes provide the grounds for bioelectronic and optobioelectronic devices. Reconstitution of apo-glucose oxidase, apo-GOx, onto a pyrroloquinoline quinone-FAD diad, assembled as a monolayer on a Au-electrode, yields an aligned bioelectrocatalytically active enzyme on the electrode surface. The resulting reconstituted enzyme electrode exhibits superior electrical contact with the electrode surface and acts as an amperometric glucose sensing electrode. The enzyme electrode operates under oxygen and is unaffected by interfering substrates such as ascorbic acid. Photoswitchable redox proteins integrated with electrode surfaces act as active systems for the amplified amperometric transduction of recorded optical signals. Chemical modification of glucose oxidase by photoisomerizable nitrospiropyran units or reconstitution of apo-GOx with a photoisomerizable nitrospiropyran FAD diad, yield photoisomerizable glucose oxidase with photoswitchable biocatalytic features. Assembly of the photoactive enzymes as monolayers on the Au-electrode results in functionalized surfaces for the cyclic 'ON-OFF' amplified amperometric transduction of recorded optical signals. A further method to photostimulate the electrical contact between a redox protein and an electrode involves the functionalization of the electrode with a photoisomerizable monolayer interface. A mixed monolayer consisting of pyridine and nitrospiropyran units was used to photoregulate the association and dissociation of cytochrome c to and from the monolayer assembly. The photostimulated electrical contact of cytochrome c with the monolayer electrode was employed to mediate the bioelectrocatalyzed reduction of oxygen in the presence of cytochrome oxidase, COx. The latter system provides an assembly for the cyclic amperometric transduction of recorded optical signals.