What is Surface Enhanced Raman Scattering (SERS)?

   The Raman scattering is a phenomena of inelastic scattering: the vibration modes  of a molecule modulate an incident laser beam and thereby are imprinted onto it. Spectrally, it observes a central peak, corresponding to the laser frequency, and set of side peaks with higher frequencies corresponding to anti-Stokes shifts, and lower frequencies corresponding to Stokes shifts. Therefore, the Raman spectroscopy can probe the structural information of the given molecule thanks to the vibrational modes of the molecular bonds. The vibration spectrum, observed by means of the Raman spectroscopy, is a stamp of a particular molecule. The main interests of the Raman spectroscopy is its utility for molecular sensing due to the abundance of laser sources, as well as of sensitive detectors operating in the visible domain. It allows extraction of the molecular structure at a high spatial resolution because of low diffraction limit at visible wavelengths. Surface enhanced Raman scattering (SERS) is one major physical phenomena of the last quarter of the twentieth century. The incident light generates plasmons in the system, and then plasmons excite molecules that generate secondary plasmons that are significantly enhanced. The radiation coming from these secondary plasmons produces the enhanced Raman signal. Thus, the intensity of SERS signal is depending on the fourth power of the local enhancement of the incident optical field. Nano- and micro-structures act as antennae efficiently amplifying the Raman signal. SERS signal is enhanced from  to . Thus, SERS effect allows detecting a weak concentration of biological and chemical molecules.