Near-field surface-enhanced Raman spectroscopy on single silver nanoparticles

We report the development of a near-field Raman microscope for nanometer-scale vibrational spectroscopy at room temperature. With the use of surface-enhanced Raman scattering and tapered single-mode fiber probes, near-field Raman spectra have been obtained from single Ag colloidal nanoparticles with excitation intensities as low as 10 nW. Far-field confocal studies have also been carried out on spatially isolated, single Ag nanoparticles. A direct comparison of the near-field and confocal results shows that near-field optical excitation does not lead to significantly different selection rules in Raman spectroscopy. This work further demonstrates that single metallic nanoparticles can be attached to the tip of a near-field probe for potential application in surface-enhanced optical microscopy and nanofabrication.