Unidirectional Photocurrent of Photosystem I on π-System-Modified Graphene Electrodes: Nanobionic Approaches for the Construction of Photobiohybrid Systems

One major vital element of the oxygenic photosynthesis is photosystem I (PSI). We report on the construction of graphene-based nanohybrid light-harvesting architectures consisting of PSI super-complexes adsorbed onto pi-system-modified graphene interfaces. The light-driven nanophotobioelectrochemical architectures have been designed on a modified carbon surface, on the basis of pi-pi-stacking interactions between polycyclic aromatic compounds and graphene. As a result of the remarkable features of graphene and the feasibility of purposeful surface property adjustment, well-defined photoelectrochemical responses have been displayed by the nanophotohybrid electrodes. In particular, the PSI graphene electrodes utilizing naphthalene derivatives provided a suitable surface for the adsorption of PSI and display already at the open circuit potential (OCP) a high cathodic photocurrent output of 4.5 +/- 0.1 mu A/cm(2). By applying an overpotential and addition of a soluble electron acceptor (methyl viologen), the photocurrent density can be further magnified to 20 +/- 0.5 mu A/cm(2). On the contrary, the investigated anthracenebased PSI graphene electrodes exhibit considerably smaller and not very directed photoelectrochemical responses. This study grants insights into the influences of different polycyclic aromatic compounds acting as an interface between the very large protein supercomplex PSI and graphene while supporting the electrochemical communication of the biomolecule with the electrode. It needs to be emphasized that solely the naphthalene-based photoelectrodes reveal unidirectional cathodic photocurrents, establishing the feasibility of utilizing this advanced approach for the construction of next-generation photovoltaic devices.