Gold nanoparticles on glass

SERS substrates fabricated using patented laser-based technology.

Applications

  • Raman spectroscopy
  • Electrochemistry
  • Chemical identification
  • Environment measurements
  • Medical diagnostics

THE PRINCIPLE OF RAMAN SPECTROSCOPY

Raman spectroscopy is a spectroscopic technique where scattered light is used to measure the vibrational energy modes of molecules, although rotational and other low-frequency modes of systems may also be observed.

When monochromatic light is irradiated on molecules, the light is scattered by molecules. Most scattered light has the same frequency with incident light but a small fraction (10-7) of the scattered light has a frequency different from the incident light due to the interaction between oscillation of light and molecular vibration (Fig. 1). Raman shifted frequency (or wavelength) depends on the vibrational state of the molecule. Stokes radiation occurs at a lower frequency (longer wavelength) compared to Rayleigh scattering, whereas Anti-Stokes radiation occurs at a higher frequency (shorter wavelength). The shift in frequency of the inelastically scattered radiation provides the chemical and structural information of the molecule.

Fig. 1. The principle of Raman scattering.

SURFACE-ENHANCED RAMAN SPECTROSCOPY 

Surface-enhanced Raman scattering (SERS) effect deals with the huge amplification of the weak Raman scattering intensity by molecules in the presence of a nanostructured metallic surface (Fig. 2).


Fig. 2. Raman scattering without (a) and with (b) nanostructured metallic surface.  

SERS is based on an enhancement of the electric field provided by the coupling of the radiation field with the localized surface plasmons of the metal nanoparticles. The electromagnetic enhancement for SERS depends on the structure of the supporting plasmonic material and theoretically can reach factors of 1010 - 1011.