NEAR-INFRARED SURFACE-ENHANCED RAMAN-SPECTROSCOPY OF CHEMISORBED COMPOUNDS ON GOLD COLLOIDS

Near-infrared surface-enhanced Raman scattering (SERS) spectra have be en measured for strongly chemisorbed compounds, such as 4-mercaptopyri dine and thiophenol, on gold colloids in mixed solvents of ethanol and water using a diode laser as an excitation source. From UV-vis spectr oscopy, the aggregated gold colloids show a broad absorbance band thro ugh the visible to the near-infrared after adding chemisorbing compoun ds. The absorption maximum is located in the range 750-850 nm, permitt ing the use of a near-IR source (826 nm) for the first time in SERS of gold colloid systems. The estimated enhancement is on the order of 10 (5). Transmission electron microscopy of aggregated gold particles rev ealed a cluster morphology. The aggregated mixed-solvent colloids were more stable than those prepared in water, and were useful in dissolvi ng compounds with poor water solubility.