MICROELECTRODE SUBSTRATES - A SOLUTION TO CURRENT PROBLEMS IN SURFACE-ENHANCED RAMAN-SPECTROSCOPY (SERS)

A simple electrochemical set-up was devised to nucleate and grow in a controlled manner a single silver nucleus, or at most very few isolated silver nuclei, on a platinum base microelectrode. Raman microscopy was used simultaneously to follow the surface-enhanced Raman signal of cyanide ions adsorbed from the plating bath onto the deposited silver. The optimum size of silver crystal which will act as a single roughness feature supporting surface-enhanced Raman scattering (SERS) can be determined from electrochemical and Raman data. The experimental conditions required to generate isolated silver crystals are discussed. The influence of the wavelength of illumination on the generation of SERS is highlighted. Once the size of the deposited silver crystal(s) has been optimized to give maximum enhancement for the combination of metal, ambient medium and wavelength of excitation selected, manufacturing a single microelectrode of corresponding dimensions or an array of microelectrodes is easy. In this way, the design of strongly enhancing SERS substrates with geometrically flat and essentially smooth surfaces can be envisaged, making any roughening step previously required unnecessary. Enhancing substrates based on smooth surfaces are expected to improve significantly the reproducibility of analyses based on SERS, paving the way towards a more general application of the technique.