REDUCTION OF FLUORESCENCE INTERFERENCE IN RAMAN-SPECTROSCOPY VIA ANALYTE ADSORPTION ON GRAPHITIC CARBON

Raman spectra of normally fluorescent materials were obtained by quenc hing the fluorescence through adsorption on carbon surfaces. Energy tr ansfer from the excited state to the carbon surface greatly reduced th e fluorescence of rhodamine 6G and the near-IR laser dye IR125, and Ra man spectra with high S/N were obtained from the adsorbed molecules. S trong resonance enhancement of Raman scattering was observed, and mono layer films of R6G were observed. R6G exhibited Langmuirian adsorption behavior, with saturation coverage occuring at similar to 0.5 mM in m ethanol. The technique was also successfully applied to bis(methylstyr yl)benzene (BMB) and fluoranthene, which are less fluorescent but also much weaker scatterers. Since the laser wavelengths yielding resonanc e enhancement are in the same range as those producing fluorescence, a dsorption to carbon permits elimination of fluorescence without loss o f resonance enhancement. The porous graphite substrate has the added a dvantage of high microscopic surface area, low elastic background, and propensity to adsorb a wide range of organic materials. With care, it was possible to observe Raman features from monolayers of materials h aving cross sections comparable to that of benzene, such as the 1205 c m(-1) peak of BMB.