Single molecule SERS: Perspectives of analytical applications

Recent developments in SERS (surface-enhanced Raman scattering) and SERRS (surface-enhanced resonance Raman scattering) spectroscopy are related to the discovery of its single molecule sensitivity. The achievement of single molecule level of SERS and/or SERRS spectral detection is understood to be conditioned by localization of detected molecules into unusually strong nanoscale-localized optical fields (dubbed hot spots). Recent calculations predict SERS enhancement factors as high as 1 × 1015 for certain chromophoric molecules located in the hot spot between two Ag nanoparticles [P. Johansson, H. Xu, M. Käll, Phys. Rev. B 72 (2005) 035427.]. Owing to a combination of single molecule sensitivity with the fingerprint selectivity inherent to vibrational spectroscopy, single molecule SERS spectroscopy can potentially offer unprecedented possibilities of analytical applications.