Anal. Chem. 1995, 67, 3154-3159
Selective Surface-Enhanced Raman Spectroscopy Using a Polymer-Coated Substrate Anjali Pal, David L. Stokes, Jean Pierre Alarie, and Tuan Vo=Dinh*
Advanced Monitoring Development Group, Health Sciences Research Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 3783 1-6101
The polymer, poly(vinylpyrrolidone), is investigated as a potential coating for alumina-based surface-enhanced Raman scattering (SERS) substrates. Description for dip coating alumina substrates with a 5%(w/v) methanolic solution of the polymer is included. Using these polymercoated substrates, various compounds, including monocyclic aromatic compounds with hydroxyl, carboxyl, and various nitrogen-based functional groups, are detected. Intensity of SERS signals from the polymer-coated substrates in comparison to that of SERS signals from uncoated substrates is demonstrated to be a function of the ana& permeabilityto the polymer coaling. Different enhancementfactors are reported for various compounds, such as benzoic acid, isonicotinic acid, and 2,4-dinitrophenol, thus indicating some enhancement selectivity of the polymer coating to various analytes. Using benzoic acid as a test compound, various coaling procedures (horizontal and vertical dipping procedures) have been evaluated. The poly(viny1pyrrolidone)-coated substrate is shown to yield a relative standard deviation in SERS signal intensity of -20%. The potential of the polymer-coated substrate as a selective detection probe is illustrated using the analyses of binary mixtures. Finally, the advantages of the polymer coating for protectingthe SERS-activelayer are also discussed.
some general models have been adopted, including chemical models of the complexation of the analyte with the atom of the metal surface3 and the formation of an "adatom" via adsorption of the analyte with the silver ~ u r f a c e . An ~ * ~electromagnetic model attributes the enhancement to the generation of intense local electric fields resulting from the excitation of the collective oscillations of conduction electrons (surface plasmons) in the metal surface.E+ While the short-range chemical effect has been described as being dependent on surface roughness at the atomic scale,4
