GATED MOLECULAR AND BIOMOLECULAR OPTOELECTRONIC SYSTEMS VIA PHOTOISOMERIZABLE MONOLAYER ELECTRODES

Molecular and biomolecular optobioelectronic systems that yield the am perometric transduction of recorded optical signals are described. Phe noxynaphthacene quinone is assembled as a monolayer on an Au electrode . Photoisomerization of the monolayer between the redox-active trans-q uinone state and the redox-inactive 'ana'-quinone state provides a mea ns to transduce electrochemically optical signals recorded by the mono layer. Coupling of the redox-active trans-quinone monolayer electrode to the secondary reduction of N,N'-dibenzyl-4,4'-bipyridinium, BV2+, p rovides a means to amplify the transduced current. As the redox potent ial of the trans-quinone monolayer is pH dependent, the electrocatalyz ed monolayer-mediated reduction of BV2+ is controlled by light and the pH. The system represents an 'AND' gated molecular electronic assembl y. A thiol nitrospiropyran monolayer was assembled on an An electrode. The functionalized electrode acts as photo-triggered 'command interfa ce' that controls the electrooxidation of dihydroxyphenylacetic acid ( DPAA). The electrical properties of the monolayer are controlled by th e photoisomer state of the monolayer and the pH of the medium. The mon olayer in the nitromerocyanine state exists at pH 9.2 and 7.0 in zwitt erionic or positively charged states, respectively. Electrooxidation o f the negatively charged substrate, DPPA, is enhanced only in the pres ence of the protonated nitromerocyanine monolayer electrode. This perm its the gated oxidation of the substrate by two complementary triggeri ng signals, light and pH. A mixed monolayer consisting of nitrospiropy ran and thiolpyridine units assembled on an Au electrode is applied as a photoisomerizable command surface for controlling the electrical co ntact of cytochrome c (Cyt c) with the electrode. In the nitrospiropyr an-pyridine configuration electrical contact of Cyt c and the electrod e is attained by the association of Cyt c to pyridine promoter sites. Photoisomerization of the monolayer to the protonated nitromerocyanine state results in the electrostatic repulsion of Cyt c from the monola yer, and the electrical contact of Cyt c with the electrode is blocked . Coupling of the electrically contacted Cyt c and nitrospiropyran-pyr idine monolayer electrode configuration to the cytochrome oxidase bioc atalyzed reduction of oxygen provides a means to amplify the transduce d amperometric response. The photostimulated association and dissociat ion of Cyt c to and from the photoisomerizable monolayer were confirme d by microgravimetric, quartz crystal microbalance analyses. The syste m mimics the function of the native vision process. (C) 1998 John Wile y & Sons, Ltd.