Evaluation techniques of bacteriorhodopsin thin films

Bacteriorhodopsin (bR) exhibits a light-driven proton pump function, and photo-sensor devices having the bR thin film show a transient photo-current signal under the on or off of photo-irradiation. Therefore, it is important to understand the orientation of bR in the thin film for fabricating such devices and elucidating the transient photo-current signal characteristics. In the present paper, we show that by second harmonic generation interference technique, the bR thin films prepared by a dip coating technique have a chiral and polar orientation with C∞symmetry. Furthermore, we discuss the absolute orientation of bRs in bR thin films.