Chalcogenide waveguide structures as substrates and guiding layers for evanescent wave Raman spectroscopy of bacteriorhodopsin

We investigate composite structures where a chalcogenide waveguide provides the substrate and the guiding layer for a bacteriorhodopsin film whose Raman spectrum is desired. Plasma exposure of the chalcogenide substrate allows for a hydrophilic surface to which organic layers can easily adhere. Surface morphology, structure, and chemical composition are characterized by X-ray photoelectron spectroscopy. A 785 nm beam from a Ti:Sapphire laser was coupled into the As2S3 waveguide and the evanescent field was employed to excite Raman scattering in the bacteriorhodopsin film. The Raman spectrum of the bacteriorhodopsin film in the fingerprint region is indicative of the native conformation and it shows that the protein is in the light adapted state.