Development of a SERS optode for the in-situ detection of chemicals in sea water

The purpose of this work is the development of a method for the in-situ detection of chemicals in sea water. Raman scattering was chosen as it is a non-intrusive method yielding finger-printing spectra of the analytes. Surface-enhanced Raman scattering (SERS) is used to provide the sensitivity necessary for trace analysis in the environment. SERS active coatings are produced by encapsulating a silver colloid in sol-gel derived xerogel films. The sol is coated onto silicon plates, microscope slides, quartz windows or optical fibers allowing a variety of measurement configurations. Results are presented for a range of aromatic hydrocarbons in sea water measured with methyl triethoxy silane (MTEOS) and ethyl triethoxy silane (ETEOS) based substrates. The suitability for operation in the marine environment is discussed in terms of selectivity, response time, limits of detection, and long term stability. Two compact marinised optodes are presented with a lensed head and a fiber head allowing for in-situ measurements in sea water with exchangeable SERS substrates or coated fibers. The optode is linked via optical fibers to an underwater core instrument containing light source and spectrograph. This is discussed in the context of a multi- disciplinary field-operable measuring device intended for operation depths up to 300 m.