This chapter starts with a brief introduction to basic Raman Spectroscopy,
its strengths and bottlenecks leading to ineffective utilization of the technique in its
conventional form. Further, the basic principle of Surface Enhanced Raman
Spectroscopy (SERS) has been discussed along with its development as a vibrational
spectroscopic tool of analytical importance. The milestones related to the development
of new methods in SERS have also been covered. The major focus of the chapter is to
describe the enhancement mechanisms responsible for magnificent enhancement
obtained in SERS as compared to normal Raman Spectroscopy. Out of various
mechanisms, the electromagnetic (EM) mechanism has been considered to play the
most significant role in enhancement. Localized Surface Plasmon Resonance (LSPR) is
chiefly responsible for the whole EM enhancement leading to E4 enhancement and
therefore, it has been discussed in detail. Other mechanisms like chemical and
electronic enhancement mechanisms have also been discussed extensively. The
dependence of SERS on various factors like substrate, excitation wavelength, size and
shape of nanoparticles, etc., has been explained with emphasis on the reported data
followed by analysis. Two photon excited SERS has been presented as a special class
of SERS. Towards the end, the application of SERS to achieve the ultimate limit of
detection by probing single molecules has been emphasised. In this context, Hot spots,
the heterogeneous nanoregions causing extremely large enhancements and their various
generations have been presented along with preliminary theoretical and experimental
results.
Keywords: Analyte, Anti-Stokes, Enhancement Factor, Enhancement Mechanism, Excitation Wavelength, Nanoparticle, Raman Scattering, Resonance, SERS Intensity, SERS Spectrum, Single Molecule etc.
