Materials. Para-nitrobenzoic acid was purchased from

citrate was purchased from VWR. All materials were used as received. Para-nitrobenzoic acid (5 mM) was prepared in ethanol (100%). Colloid preparation. Silver colloid was prepared using the method of Lee and Meisel8 with slight alterations; silver nitrate (0.05-0.06 g) was dissolved in deionized water (500 mL) and sodium citrate (5.0 mL, 1.0 mL/min) was added once the solution was boiling. The resulting colloids were yellow-brown with an extinction maximum near 420 nm. Alloy colloids were prepared using the method of Link et al.9 with slight alterations; chloroauric acid (1.0 mM) and silver nitrate (1.0 mM) were used (total of 0.025 mmoles metal). The total volume was brought to 75 mL and the solution was heated. Once boiling, sodium citrate (5.0 mL) was added and boiled (30 min). Colloidal metal film preparation. Silver nanoparticle slide preparation was adapted from Natan.10 Quartz, ITO and glass slides were cut and immersed in piranha (1 part H2O2 (35%): 4 parts conc. H2SO4) for cleaning (10-15 min). The slides were rinsed well with methanol and soaked in silane solution (4 parts 3-aminopropyl tri-methyloxysilane: 1 part methanol) for 48 h. After rinsing with methanol again, the slides were individually placed in vials with colloid for 24 h and were rinsed with deionized water. Instrumentation. Absorbance spectra were acquired for colloids and metal films. Raman spectra were obtained with a custom-built Raman spectrometer (532 nm, 150 mW, 50 μm slits). Spectra were analyzed using Origin (OriginLab