Enhanced Electronic Conductance across Bacteriorhodopsin, Induced by Coupling to Pt Nanoparticles

Studying solid-state electronic conductance of biological molecules requires interfacing the biomolecules with electronic conductors without altering the molecules. To this end, we developed and present here a simple, solution-based approach of conjugating Bacteriorhodopsin (bR)-containing membranes with metallic clusters. Our approach is based on selective electroless deposition of Pt nanoparticles on suspended membrane fragments through chemical interaction of the Pt precursor with the protein's residues. Optical absorption measurements show that the membranes retain their photoactivity after this procedure. The result of the Pt deposition is best shown by conductive probe atomic force microscopy mapping of electronic current transport across such soft biological layers, which allows reproducible microscopic electrical characterization of the electronic conductance of the resulting junctions. The maps show that chemical contact between the protein and the deposited electrode yields better electronic coupling than a physical contact, demonstrating that also with biomolecules, the type and method of deposition of the electrical contact are critical to the behavior of the resulting junctions.