Non aggregated colloidal silver nanoparticles for surface enhanced resonance Raman spectroscopy.

Silver nanoparticles with a tuneable λ max were produced as colloids by heterogeneous nucleation. The synthesis process is both fast and repeatable, producing stable PVA capped nanoparticles. The colloid's effectiveness in the SERRS system was investigated using Rhodamine 6G, R6G, Crystal Violet, CV, and Malachite Green, MG, as probe molecules. A clear sensing trend was observed, where the Raman signal emitted was significantly enhanced by the addition of silver nanoparticles. A build up of signal intensity is observed until an optimum ratio is achieved, followed by a decline in signal intensity as the concentration of nanoparticles is further increased. The sensing trend appeared to be dependant on the structure of these model molecules with similarly structured compounds exhibiting similar trends. Thus a maximum enhancement with the Ag: analyte molar ratio of ∼ 5.56: 1, was seen for CV and MG whereas R6G had a maximum enhancement at the Ag: analyte molar ratio of ∼ 2.25: 1.