Authors: S. Crittenden, J. Hillebrecht, S. Howell, R.R. Birge and R. Reifenberger
Affilation: Purdue University, United States
Pages: 424 - 427
Keywords: bacteriorhodopsin, biomembrane, SPM, photovoltage
Bioelectronics offers a potential alternative to Si-based technology because natural evolution and selection have optimized many biological molecules to perform tasks that can only be mimicked by complicated electronic circuits. Purple membrane (PM) patches containing bacteriorhodopsin (bR) proteins could be harvested from the bacterium and used as the key light-absorbing unit in nanometer-size photodetectors that rely on many of the light sensitive properties inherent in the protein [1-7]. We used non-contact scanning probe microscopy to characterize bR films on multiple substrates. Wild type and a variety of mutants were studied. Conductive AFM was used to probe the I(V) characteristics of individual PM patches. Electrostatic force microscopy techniques were developed to study the photovoltage of PM multilayers on indium tin oxide substrates. We find a humidity dependant photovoltage response under illumination by a 635 nm photodiode with peak photovoltages in excess of 2V at ~140 W/m2 for ~15% relative humidity. I(V) data from individual PM patches show evidence for threshold conduction dependant on the relative humidity. Morphological studies show reduced structural stability of membrane patches for all mutants investigated. Taken together, these results reveal many new characteristics of bR that may be of significance for the design of future nanoscale devices.