Charge transport in purple membrane monolayers: A sequential tunneling approach

Current-voltage (I-V) characteristics in proteins are sensitive to conformational changes induced by an external stimulus (photons, chemical, etc.). This sensitivity can be used in medical and industrial applications as well as shedding new light on the microscopic structure of biological materials. Here, we show that a sequential tunneling model of carrier transfer between neighboring amino acids in a single protein is the basic mechanism responsible for the electrical properties measured over a wide range of applied potentials. We also show that such a strict correlation between the protein structure and the electrical response can lead to a new generation of nanobiosensors that mimic the sensorial activity of living species. To demonstrate the potential usefulness of protein electrical properties, we provide a microscopic interpretation of recent I-V experiments carried out in bacteriorhodopsin at a nanoscale length.