Surface-enhanced Raman spectroscopy (SERS) is a spectroscopic technique used to enhance the intensity of the Raman signal by the amplification of the electromagnetic field of the incident and/or scattered light with metallic nanoantennas. The amplification can reach even 5-6 orders of magnitude resulting in highly sensitive and fast Raman detection. SERS requires nanoantennas (realized in the form of gold or silver nanoparticles or nanostructures of various shape and size) resonantly tuned to the energy of incident and/or scattered photons. The amplification is limited to the close vicinity of the nanoantennas, therefore, SERS requires close contact or even adsorption of the sample on their surface. With its proven single-molecule detection capabilities SERS is widely used in trace material analysis, forensics, medical diagnostics, food and water quality control, detection of explosives, viruses, bacteria and other dangerous materials.
Raman spectroscopy is an efficient light scattering technique that can be used to determine the vibrational modes of molecules, crystals, amorphous materials, etc. in solid, liquid and gaseous form. It characterizes the structure and bonding configuration through inelastic light scattering during which the incident photon excites/annihilates a vibrational mode of the medium resulting in a scattered photon of different energy. The energy difference of the two photons corresponds to the energy of the excited/annihilated vibration. A Raman measurement is realized through the excitation of the sample with monochromatic light (laser) and the recording of the spectrum of the scattered light in wavelength regions different from the excitation. Nowadays, Raman spectroscopy is utilized in a large variety of applications including medical diagnostics, biophotonics, biology and nanomedicine, environmental protection, quality monitoring, and temperature and internal stress measurements.