We demonstrate single-molecule-level features using near-field optical microscopy on bacteriorhodopsin (bR), a membrane protein that functions as a light-driven proton pump. The photophysical properties of bR are utilized in this imaging technique, using a combination of photoexcitation sources, to accurately identify the active regions and quantify the optical parameters. The studies of bR monolayers are carried out on inert quartz substrates as well as active conducting polymer (polyaniline) substrates. The substrate also plays an important role in the photocycle quantum efficiencies. We speculate on mechanisms governing the higher near-field absorption strength of bR molecules.
© 2010 Optical Society of America
Original Manuscript: October 22, 2009
Revised Manuscript: January 15, 2010
Manuscript Accepted: January 18, 2010
Published: February 24, 2010
Vol. 5, Iss. 6 Virtual Journal for Biomedical Optics
Narasimhan Arun, Sabyasachi Mukhopadhyay, and K. S. Narayan, "Monitoring intermediate states of bacteriorhodopsin monolayers using near-field optical microscopy," Appl. Opt. 49, 1131-1138 (2010)