Remarkably enhanced photoelectrical efficiency of bacteriorhodopsin in quantum dot – Purple membrane complexes under two-photon excitation

Abstract

The photosensitive protein bacteriorhodopsin (bR) has been shown to be a promising material for optoelectronic applications, but it cannot effectively absorb and utilize light energy in the near-infrared (NIR) region of the optical spectrum. Semiconductor quantum dots (QDs) have two-photon absorption cross-sections two orders of magnitude larger than those of bR and can effectively transfer the up-converted energy of two NIR photons to bR via the Förster resonance energy transfer (FRET). In this study, we have engineered a photoelectrochemical cell based on a hybrid material consisting of QDs and bR-containing purple membranes (PMs) of Halobacterium salinarum and demonstrated that this cell can generate an electrical signal under the two-photon laser excitation. We have shown that the efficiency of light conversion by the PM–QD hybrid material under two-photon excitation is up to 4.3 times higher than the efficiency of conversion by PMs alone. The QD integration into the bR-containing PMs significantly improves the bR capacity for utilizing light upon two-photon laser excitation, thus paving the way to the engineering of biologically inspired hybrid NIR nonlinear optoelectronic elements. The nonlinear nature of two-photon excitation may provide considerable advantages, such as a sharp sensitivity threshold and the possibility of precise three-dimensional location of excitation in holography and optical computing.