Optical Properties of Bacteriorhodopsin–Gold Bionano Interfaces

Monolayers of different mutants of bacteriorhodopsin (bR) with purple membranes are deposited on gold (Au) substrates. Optical measurements and density functional theory-based electronic structure calculations are reported for the first time for the bR chromophore, which is the retinal protonated Schiff base. The dielectric function of the chromophore is extracted using spectroscopic ellipsometry. Designed mutants of bR are used to investigate the bonding with the gold substrate and bR–Au bonding changes can be tracked using the optical properties of the retinal fragment.