Fiber-optic SERS sensor with optimized geometry

A novel surface enhanced Raman scattering (SERS) sensor has been developed and built. This sensor uses an “optrode” configuration in which a single optical fiber transmits both the exciting laser radiation and the SERS signal from the molecules adsorbed onto the SERS active substrate. The main advantage of this sensor is its unique geometry which can be obtained by means of a double static etching process achieved with a 40% hydrofluoric acid aqueous solution covered with an organic solvent over-layer. The SERS active substrate is prepared by a standard process of immobilizing silver nanoparticles with 3-aminopropyltrimethoxysilane. The optimized geometry permits attainment of the best limit of detection (LOD) value ever reported in the literature for a fiber-optic SERS sensor. In particular, we are able to record SERS spectra from a 10−9 M (0.018 ppb) solution of crystal violet in distilled water both with measurements performed in solution and with a “dip and dry” technique. Moreover, the capability to detect molecules such as crystal violet at such very low concentrations make this SERS sensor very promising for monitoring the diffuse illicit use of this molecule in aquaculture industry.