(699j) Delta- and Proteorhodopsin-Based Bionanoelectronic Devices for Light-Controlled Conversion of Protonic to Electronic Currents

The burgeoning field of bionanoelectronics aims at interfacing biology with electronics through the use of bio-based or biocompatible nanomaterials. A particular area of interest is the controlled conversion of ubiquitous biological ionic gradients into electrical signals that can be read or processed by conventional electronics. Here, we describe the efficient integration of proton-transporting rhodopsins with palladium (Pd) contacts to achieve light-activated conversion of protonic currents into electronic signals. The process involves engineering archaeal or proteorhodopsins with a Pd-binding peptide in order to bring the proton exit site in close proximity to the electrode; using protein and folding engineering strategies to express high levels of functional rhodopsins that are activated at various wavelengths; optimizing the integration and orientation of these proteins in liposomes; and forming supported bilayers on Pd/PdHx microfluidic devices fabricated by photo- and soft lithography. We demonstrate that addition of a Pd-binding extension leads to a nearly one order of magnitude increase in electronic signal with light-controlled â??onâ? and â??offâ? responses that are complete in seconds, discuss the development of steady state currents and describe devices in which proton transport and the corresponding electronic responses are selectively activated by different wavelengths of light.