Chapter 6 Single molecule sensitivity in surface enhanced Raman scattering using surface plasmon

Abstract

It is crucial to elucidate the nature of constituents at an atomic or molecular scale to realize a bottom-up nanotechnology, for example, a single molecule device or a nano-chemical factory. Surface enhanced Raman scattering (SERS) available under ambient conditions even at the solid/liquid interfaces attracts increasing interest according to the potentialities of single molecule sensitivity (SMS) and also nanoscale spatial resolution when combined with near-field microscopy. SERS is a well-known phenomenon for more than 30 years that Raman signal from adsorbates on roughened metal surfaces is enhanced by a factor of 104–106 caused by excitation of surface plasmon polariton (SPP) on roughened metals and/or by the “first layer” enhancement including charge transfer resonance between adsorbates and metals. The enhancement factor obtained with a conventional Raman spectroscopy is a population-averaged value for enormous molecules sitting on numerous Ag particles with various shapes and sizes, and thus insufficient to yield single molecule detection (SMD) in SERS. Recent progress in scanning probe microscopy (SPM) in addition to a highly-sensitive charge-coupled device (CCD), detector enables to observe extremely weak spectral signal from an individual metal particle or even from single molecule.