CONTRIBUTIONS OF SHORT-RANGE AND CLASSICAL ELECTROMAGNETIC MECHANISMS TO SURFACE-ENHANCED RAMAN-SCATTERING FROM SEVERAL TYPES OF BIOMOLECULES ADSORBED ON COLD-DEPOSITED ISLAND FILMS

Surface-enhanced Raman scattering (SERS) spectra of three different classes of adsorbates have been analyzed: (1) native and denatured calf thymus DNA and adenine, as examples of molecules with electronic transitions in the UV region only; (2) flavine adenine dinucleotide (FAD) and doxorubicin (DOX), as examples of chromophores with low extinction transitions in the visible region; and (3) beta-carotene, as an example of a chromophore with a very high extinction coefficient for an electronic transition in the visible region. These molecules were adsorbed on silver island films that had an extinction maximum in the 450-660 nm region of the electromagnetic spectrum. The short-range mechanism of Raman enhancement has been demonstrated to contribute primarily to enhanced Raman scattering from molecules in groups 1 and 2, whereas the pure (classical) electromagnetic mechanism dominates the enhancement of beta-carotene resonance Raman scattering.