Methods and apparatus are provided for detecting one or more contaminant particles in an environment with an optical sensor. The sensor includes at least one optical waveguide in a resonant arrangement and a light source positioned in an environment in which the presence of a contaminant particle is sought to be determined. The at least one optical waveguide is of a diameter that an evanescent tail of the lightwave extending there through extends into the environment and is reactive to at least one contaminant particle in the surrounding environment. A detector is positioned to receive light indicative of the sharpness of the optical resonance lineshape of the optical resonator at a pre-selected optical wavelength. The detected information determines the specific contaminant particle in the environment and the concentration of the contaminant particle in the environment.