Characterization of protein monolayers by surface plasmon resonance combined with cyclic voltammetry 'in situ'

Surface plasmon resonance (SPR) and cyclic voltammetry (CV) have been used to characterize monolayers of cytochrome-c and cytochrome-c-oxidase adsorbed on gold surfaces modified with several alkanethiol self-assembled monolayers. A direct comparison between protein surface coverages calculated from SPR and cyclic voltammetric measurements carried out with the same sample allows one to make some conclusions about the amount and orientation of cytochrome-c adsorbed on the gold surface. Time differential surface plasmon resonance measurements combined with cyclic voltammetry 'in situ' has been used to investigate the redox processes of adsorbed cytochrome-c and cytochrome-c-oxidase. The potential-dependent time differential SPR response observed for cytochrome-c adsorbed on Au\MPA (3-mercapto-1-propionic acid) electrodes is explained as arising from a potential-dependent adsorption/desorption process. By contrast, similar experiments carried out with cytochrome-c oxidase adsorbed on Au\MPA electrodes can be explained as the result from a potential-dependent conformational change between the 'resting' and the 'pulsed' states of the adsorbed oxidase. (C) 1999 Elsevier Science S.A. All rights reserved.