A simple method to fabricate silver colloid clusters for surface-enhanced Raman scattering

We have developed a simple method to fabricate silver colloid clusters for surface-enhanced Raman scattering (SERS). When colloid particles were immobilized on poly(4-vinyl pyridine) (PVP) films, most of them were immobilized individually. However, the formation of silver colloid particle clusters occurred following a three-step process: immobilizing colloid particles on PVP films, adsorbing target molecules (adsorbates) on the immobilized particles, and then immobilizing colloid particles again. The calculated enhancement factor was approximately 1 × 106, which is about 72 times higher than that measured without doing the second immobilization. Our method is relatively simple and inexpensive with respect to fabricating SERS substrates.