Surface-Enhanced Raman Scattering Spectroscopy of Photosynthetic Membranes and Complexes

Surface-enhanced Raman scattering (SERS) results when ion complexes, molecules, or chromophores adsorbed onto or near roughened silver, gold, or copper substrates are excited with laser light. Surface enhanced resonance Raman scattering (SERRS) occurs when the laser excitation wavelength is in resonance with an electronic transition in the adsorbate and provides additional enhancement. The major advantages of SERS/SERRS include extreme analytical sensitivity, molecular selectivity, minimization of fluorescence, and distance sensitivity. SERRS has considerable potential for analytical applications and for fundamental studies of biomolecular structure on surfaces. Membrane studies suggest that SERRS can provide qualitative information about the location and orientation of chromophores within the membrane. Future developments should include the use of new detectors, which have very low dark counts and can be used to integrate signals for long time periods. It should be possible to obtain unenhanced Raman spectra on any surface using this approach. Also, the use of new lasers, such as the titanium: sapphire laser allows excitation throughout the red region of the electromagnetic spectrum (650–1000 nm). This is valuable for studies of biological samples on gold substrates.