Fiber optic sensor based on gold island plasmon resonance

A fiber optic chemical sensor based on gold-island surface plasmon excitati on is presented. The sensing part of the fiber is a one inch portion on whi ch cladding has been removed and onto which a thin layer of gold has been d eposited to form a particulate surface. Annealing the gold reshapes the par ticles and produces an absorbance near 535 nm when the only medium residing outside the surface is air. A range of wavelengths provided by a white lig ht source and monochromator is launched through the optical fiber. The tran smitted spectra display shifts in the resonance absorption due to any chang es in the medium surrounding, or adsorbed onto the fiber. Experimental resu lts for the sensitivity and dynamic range in the measurement of liquid solu tions are in agreement with a basic theoretical model which characterizes t he surface plasmon using nonretarded electrodynamics. Furthermore, the mode l assumes the particles are isolated oblate spheroids with a distribution o f eccentricities. (C) 1999 Elsevier Science S.A. All rights reserved.