Five surface-enhanced Raman scattering (SERS) substrates were quantitatively compared for ease of preparation, sensitivity, limit of detection (LOD), reproducibility, and stability. Specifically, vapor-deposited Ag films, electrochemically roughened Ag electrodes, nitric acid-etched Ag foil, Tollens-produced Ag films, and photore-duced Ag films on TiO2 were examined. Of these substrates, post-deposition-annealed Ag films exhibited the greatest sensitivity and lowest LOD, with 152 ± 1 counts per femtomole and an LOD of 0.36 ± 0.02 femtomoles of trans-1,2-bis(4-pyridyl)ethene (BPE). The substrate demonstrating the poorest sensitivity and highest LOD was Ag deposited from the Tollens reaction, with 0.38 ± 0.01 counts per femtomole and an LOD of 270 ± 20 femtomoles of BPE. The easiest substrate to prepare, nitric acid-etched Ag foils, exhibited a sensitivity of 0.485 ± 0.008 counts per femtomole and an LOD of 200 ± 10 femtomoles of BPE.

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The presence of carbonaceous contamination on common surface-enhanced Raman scattering (SERS) surfaces has been a primary limitation to the analytical utility of SERS; background contamination significantly affects reproducibility and often determines the limit of detection. Due to the strong interaction between thiols and Ag or Au, self-assembly of alkanethiols onto these metals results in the displacement of "adventitious material" from the metal. The cleaning procedure presented here utilized self-assembly of decanethiol on an electrochemically roughened Ag foil for removal of surface contamination. The self-assembled layer was subsequently removed by rapid oxidation with ozone, followed by rinsing in methanol. The clean Ag surface exhibited a tremendously improved background and a 3-fold increase in the enhancement factor for a probe molecule.

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Raman spectra of molecules adsorbed on metal colloids exhibit large signal enhancements over those of the pure or solution phase samples. This paper presents background information on surface-enhanced Raman spectroscopy (SERS) and provides details for carrying out an SERS experiment in the undergraduate physical chemistry laboratory. A single system, pyridine on silver, has been adapted from the research literature for use with undergraduates. Instructions for sample preparation, experimental setup, and data analysis are provided in addition to sample spectra.