Tailor-made metal nanoparticles as SERS substrates

In this contribution we summarize recent experiments with the objective to generate optimized substrates for surface-enhanced Raman spectroscopy (SERS). For this purpose, the well-established laser-assisted growth technique has been applied, which relies on a precise control of the growth kinetics of supported metal nanoparticles. With this method reproducible and stable SERS substrates with tailor-made optical properties possing best field enhancements were produced for specific excitation wavelengths and detection ranges. Optimization of the SERS substrates has been achieved by stabilizing the localized surface plasmon polariton resonance (SPR) of gold nanoparticles in the vicinity of the laser wavelength of lambda=647 nm and lambda=785 nm used for SERS excitation. After nanoparticle preparation, SERS spectra of pyrene were obtained using naturally grown nanoparticles and nanoparticles prepared by laser-assisted growth. The most important result is that the optimized substrates prepared by laser-assisted growth exhibit a significantly higher signal-to-noise ratio as compared to naturally grown nanoparticles. They are even better than substrates whose SPR has been tuned to the excitation wavelength by an elevated temperature during preparation. Another important observation is that all SERS spectra exhibit excellent reproducibility and the substrates do not show degradation during the measurements. Finally, the SERS enhancement factors due to the optimized substrates have been estimated and are on the order of 10(5) to 10(6).