Optical organophosphate sensor based upon gold nanoparticle functionalized fumed silica gel

We report on the creation of a high surface area, chemically selective material for the efficient adsorption of organophosphate and organophosphonate species. Using silica microparticles in conjunction with gold nanoparticles and surface modification chemistry, we have demonstrated a material with a binding constant for organophosphonates and organophosphates (OPPs) of K=2x10(6) M-1. The binding of OPPs to the modified gold nanoparticles appears as a spectral shift in the gold nanoparticle resonance. The sensitivity of this technique is limited by scattering losses of suspensions of the particles, and we report on how this sensitivity can be recovered to a significant extent by the use of solvents with a refractive index close to that of the silica particles.