SERS substrates produced by tailor-made metal nanoparticles

Abstract

In this contribution, we present new tailor-made substrates for surface-enhanced Raman scattering (SERS). They are based on precise control of the mean shape and the average diameter of nanoparticles prepared by self-assembly of atoms on dielectric supports. Tailoring of the SERS substrates have been achieved by precise tuning of the localized surface plasmon polariton resonance of silver nanoparticles to the vicinity of the laser wavelength used for SERS excitation. The underlying method relies on control of the growth kinetics of supported metal nanoparticles which causes a pronounced shape change as a function of particle size. Additionally, the strong dependence of the energetic position of surface plasmon excitation on the shape of the particles is exploited. With this preparation method, SERS substrates with optimized plasmon resonances and field enhancement can be easily produced for specific excitation wavelengths and detection ranges. The nanoparticles have been characterized by optical spectroscopy and atomic force microscopy (AFM). Silver nanoparticles with a plasmon resonance at about 2.4 eV were prepared with and without a protective CaF 2 coating. SERS spectra of pyrene were obtained with excitation at 514.5 nm. They exhibit a good reproducibility. Furthermore, the substrates did not show degradation during the measurements and those with protective coating still yielded 70% of the SERS intensity of uncoated substrates, indicating their potential usefulness for an analytical detection of specific molecules. Further tailoring of supported metal nanoparticles for SERS applications by laser irradiation will be discussed.