RETRACTED: Monolayers of pigment-protein complexes on a bare gold electrode: Orientation controlled deposition and comparison of electron transfer rate for two configurations

Photosynthetic protein complexes are very efficient in solar energy absorption, excitation transfer, and subsequent electron transfer. These complexes have the potential to be exploited as circuit elements for various bio-hybrid devices, ranging from biosensors to solar cells. In this report, we characterized a bioelectronic composite fabricated by interfacing reaction center-light harvesting 1 (RC-LH1) complex with an un-functionalized gold surface in defined orientation. The orientation of RC-LH1 complex was controlled by using Langmuir-Blodgett (LB) deposition technique: RC-LH1 complexes were attached to the electrode facing either with their primary donor or the acceptor sides by'"forward" or'"reverse" dipping, respectively. Photochronoamperometry was utilized to confirm the integrity of the protein complexes and their orientation. Electrical transport of protein complexes coupled to gold electrode was studied by using conductive atomic force microscopy (C-AFM). Two distinct current-voltage (I-. V) curves were observed for two different deposition schemes, indicating opposite orientations of RC-LH1 complexes on the electrode. I-. V spectroscopy was also carried out under light illumination, the magnitude of current was considerably increased by the light illumination and the asymmetry of the curves was more pronounced. We show that, RC-LH1 complexes attached to the electrode with primary donor side facing the electrode exhibit much faster electron transfer compared to opposite orientation.