title: Plasmonic field enhancement of the bacteriorhodopsin photocurrent during its proton pump photocycle.
abstract: The proton pump photocycle of bacteriorhodopsin (bR) produces photocurrent on a microsecond time scale which is assigned to the deprotonation step forming the M(412) intermediate. The return of the M(412) intermediate to the bR ground state (bR(570)) has two pathways: (1) thermally via multiple intermediates (which takes 15 ms) or (2) by a more rapid and direct process by absorbing blue light (which takes hundreds of nanoseconds). By using nanoparticles (Ag, Ag-Au, and Au NPs) having different surface plasmon resonance extinction spectra, it is found that Ag NPs whose spectrum overlaps best with the M(412) absorption regions enhance the stationary photocurrent 15 times. This large enhancement is proposed to be due to the accelerated photoexcitation rate of the M(412) (in the presence of the plasmon field of the light in this region) as well as short-circuiting of the photocycle, increasing its duty cycles.
authors.affiliation: Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive, Atlanta, Georgia 30332, USA.
authors.forename: Chun-Wan
authors.initials: CW
authors.lastname: Yen
authors.forename: Li-Kang
authors.initials: LK
authors.lastname: Chu
authors.forename: Mostafa A
authors.initials: MA
authors.lastname: El-Sayed
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000528:radiation effects; D006047:Gold Alloys / Q000138:chemical synthesis / Q000737:chemistry*; D008027:Light; D053768:Metal Nanoparticles / Q000737:chemistry*; D055668:Photochemical Processes; D017494:Proton Pumps / Q000737:chemistry; D012834:Silver / Q000737:chemistry*; D020349:Surface Plasmon Resonance
chemical_list: D006047:Gold Alloys; D017494:Proton Pumps; D012834:Silver; D001436:Bacteriorhodopsins