The preparation and performance of a silver nanoparticle-based sensor for use in Oddy tests are reported. A suspension of spherical silver nanoparticles (Ag NPs) (mean diameter of 30 nm, absorption of surface plasmon resonance (SPR) at 428 nm) in a methanol was synthesized and the Ag NPs were assembled into monolayer films on glass slides, using a polyethylenimine as a linking agent. UV-Vis spectrophotometry was employed to measure the SPR intensity of the Ag NP films in order to evaluate the extent of reaction. It was observed that the Ag NP films were quite stable under Oddy test conditions in a blank test, after a brief alteration of the spectrum due to particle dispersal, with no significant decrease in the SPR intensity after 1.5 months at 60[degree]C and 100% RH. The sensitivity of Ag NP films to sulfide gases emitted from a test wool fabric in the Oddy test was investigated. UV-Vis spectra taken after the Oddy tests showed the disappearance of the Ag NP SPR peak and the growth of the UV absorption due to Ag2S. Elemental analysis with energy dispersive x-ray spectroscopy confirmed that sulfur had been incorporated into the Ag NP film. Ag NP assemblies of lower NP density were created that indicated the presence of sulfide gases prior to significant tarnishing of a Ag foil. The results demonstrate that the Ag NP films can be used as sensitive, quantitative optical sensors to replace Ag foils in the Oddy test system.