Coulomb blockade effect and negative differential resistance in the electronic transport of bacteriorhodopsin

A functional protein of bacteriorhodopsin has been employed for an approach to develop molecular single-electron transistors. A purple-membrane nanofragment shows a characteristic, cyclic, and reproducible I-V curve having negative differential resistance and an on-off peak-to-valley ratio of 660. The conductance increases exponentially with temperature increase with an activation energy of 47 meV, comparable to the charging energy of a bacteriorhodopsin molecule. This with observed I-V scaling relationship indicates that the Coulomb blockade is the primary conductance-limiting feature and that charges are carried by arrayed Coulomb islands of bacteriorhodopsin.