Surface Enhanced Raman Spectroscopy: Using Metal Nano-structured Substrates for Ultra-sensitive Detection

摘要

Surface Enhanced Raman Spectroscopy (SERS) has the potential forextending the limit of detection in chemical analysis to a single molecule. Realization of such an effect depends on many factors including good adsorptivity of the nano-structured metal surface for the target molecules, matching of molecular dimensions with that of the surface roughness and a resonance between the surface plasmon and the exciting laser field. We report some work from our laboratories on surface preparation for SERS and its prospect for practical utilization. Since the first observation of the SER effect in the early 1980s there has been much research activity into many aspects of the phenomenon. Although detection of the Raman signal has been reported from a single molecule adsorbed on metal colloid particles having dimensions smaller than the wavelength of the exciting laser field [2, 3], a satisfactory explanation of the effect either for colloids or for metallic nano-structures on solid surfaces remains elusive. This is primarily due to the complexity of the charge-dependent adsorption of the target species onto the nano-structured and high-conductivity (coinage) metal surface and the difficulty of matching the dimension of the surface (or colloidal) structure with that of the target molecule. Also important is the setting up of a resonance between the 'surface plasmon' and the laser field, which is governed by the complex dielectric properties of the metal at the excitation wavelength. The requirement for rapid, minimally invasive in-situ monitoring of concealed explosives and contraband at check points has prompted research both at our laboratories and elsewhere into the evaluation of the SERS technique for such purposes.