Biomolecular Electronic Device Applications of Bacteriorhodopsin

Over the last thirty years, bacteriorhodopsin has become one of the most actively researched proteins in biochemistry and biophysics. Interest in this protein stems not only from its unique photochemistry as a light-driven proton pump, but also from its potential as an active component of biomolecular device applications. Architectures for devices that range in form and function from polymer film based holographic interferometers to three-dimensional optical memories have been proposed and built. Bacteriorhodopsin’s propensity for biomolecular optics and electronics is due to three main light-induced responses: (1) A light-induced photocycle that consists of a variety of photochemically-distinct intermediates characterized by shifted absorption maxima, (2) A branched photocycle that results in a permanent blue shifted intermediate, and (3) A complex time-dependent photoelectric response that varies in both sign and amplitude over several orders of magnitude. These properties will be discussed below, as relevant to the development of two specific bacteriorhodopsin applications: the branched photocycle three-dimensional optical memory and the holographic associative memory.