Orientated binding of photosynthetic reaction centers on gold using Ni-NTA self-assembled monolayers

Coupling of photosynthetic reaction centers (RCs) with inorganic surfaces is attractive for the identification of the mechanisms of interprotein electron transfer (ET) and for possible applications in construction of photo- and chemosensors. Here we show that RCs from Rhodobacter sphaeroides can be immobilized on gold surfaces with the RC primary donor looking towards the substrate by using a genetically engineered poly-histidine tag (His(7)) at the C-terminal end of the M-subunit and a Ni-NTA terminated self-assembled monolayer (SAM). In the presence of an electron acceptor, ubiquinone-10, illumination of this RC electrode generates a cathodic photocurrent. The action spectrum of the photocurrent coincides with the absorption spectrum of RC and the photocurrent decreases in response to the herbicide, atrazine, confirming that the RC is the primary source of the photoresponse. Disruption of the Ni-NTA-RC bond by imidazole leads to about 80% reduction of the photocurrent indicating that most of the photoactive protein is specifically bound to the electrode through the linker.