Remote Detection using Surface Enhanced Resonance Raman Scattering
Ailie McCabe, W. Ewen Smith, Grant Thomson*, David Bachelder*,
Geoffrey Ashcroft†, and Brian F. Foulger‡.
Department of Pure and Applied Chemistry, University of Strathclyde,
295 Cathedral Street, Glasgow, G1 1XL, UK.
*Department of Physics and Astronomy, Molecular Physics and Instrumentation Group, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK.
†MOD, P.O. BOX 1666, London, SW1P 1XB, UK.
‡CBD Environmental Services, Building C34, DERA Winfrith,
Winfrith Technology Centre, Dorcester, Dorset, DT2 8XJ, UK.
Surface enhanced resonance Raman scattering (SERRS) provides intense Raman signals which are shown here to be stable in a target and to be detectable at least 10 metres from the spectrometer. The results indicate that SERRS labelling 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 polyvinyl 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 metre from the probe head. The intensity of the scattering from samples kept in the dark showed little change over a period of four weeks. However, when the samples were left in direct sunlight, the scattering intensity dropped significantly over the same period but could still be determined after one year. 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 fibre optically coupled to the spectrometer. Effective detection of SERRS was obtained 10 metres from the spectrometer using 3.6 mW of power and a 20 second accumulation time.