New Method for Obtaining Raman Spectra of Extremely Small Quantities of Light-Absorbing Substances Adsorbed on Silver from Very Dilute Solutions

摘要

Micro-Raman spectra of picogram to sub-femtogram quantities of several chromophoric substances adsorbed from dilute solution on silver were measured and compared with similar measurements on some non-chromophoric substances. The silver surface enhanced resonance Raman measurements require no redox roughening of the surface, sometimes no applied potential and only 1-2 mW of defocused laser power. The new method by which silver surface enhancement is achieved requires contact of the surface with halide ion solution for several hours. The most astounding results thus far were achieved with 1,1′-diethyl-2,2′-cyanine iodide (2,2′-cyanine). Raman spectra of the adsorbate from 20 ml of 1 x 10 ~(-17) M solution of the dye were measured using the method. Further characteristics of the phenomenon were obtained based on extensive Raman measurements on 2,2′-cyanine. Some further details resulting from these measurements are described.