Remote detection using surface-enhanced resonance Raman scattering

Surface-enhanced resonance Raman scattering (SERRS) provides intense Raman signals that are shown here to be stable in a target and to be detectable at least 10 meters from the spectrometer. The results indicate that SERRS labeling of objects and their detection at a distance with a low-power laser is feasible. Rhodamine and a dye specifically designed to give good surface adhesion, [4(5'-azobenzotriazyl)-3,5-dimethoxyphenylamine] (ABT DMOPA), were adsorbed onto silver particles and the particles dispersed in poly(vinyl acetate) (PVA) and varnish. SERRS from rhodamine was not detected from colloid dispersed either in PVA or varnish, presumably due to displacement of the dye from the silver surface. ABT DMOPA gave good SERRS. Maps of the SERRS intensity of films indicated variability of 10-20% if ultrasound was applied to improve dispersion during mixing. Scattering performance was evaluated using a system with the sample held up to one meter from the probe head. The intensity of the scattering from samples kept in the dark showed little change over a period of up to one year. However, when the samples were left in direct sunlight, the scattering intensity dropped significantly over the same period but could still be determined after eight months. An optical system was designed and constructed to detect scattering at longer distances. It consisted of a probe head based on a telephoto or CCTV lens that was fiberoptically coupled to the spectrometer. Effective detection of SERRS was obtained 10 m from the spectrometer using 3.6 mW of power and a 20 s accumulation time.