Optimized recipe for sol-gel-based SERS substrates

The aim of this study was to develop further surface-enhanced Raman scattering (SERS) substrates appropriate for the in situ environmental determination of chemicals in sea-water important for global environmental problems. By encapsulating silver colloids in a sol–gel-derived xerogel, SERS-active coatings were produced with the high mechanical and chemical stability required for underwater field measurements. A flow-through system was used which simulates measurements under real flow conditions. Substrates were optimized regarding sensitivity to different analytes and long-term stability by varying solvent type, pH and sol–gel precursors. The substrates were characterized by their SERS activity and calibration functions of the Langmuir isotherm type were found for a variety of aromatic hydrocarbons. Limits of detection as low as 9 ppb for phenylacetylene and 135 ppb for biphenyl were achieved. Detailed tests on long-term stability in sea-water yielded a substrate half-life of 13 days, which resulted in a substrate lifetime of at least 5 weeks. Copyright © 2000 John Wiley & Sons, Ltd.