Apparatus and method are provided for chemical and biological agent sensing. The sensing apparatus includes a resonator having a resonance frequency and one or more optical fiber coils. The optical fiber coil has a permeable cladding and an indicator embedded in the cladding that reacts to an agent (e.g., a chemical or biological substance). The resonator circulates light through the coil and produces a resonance shape centered at the resonance frequency and measured via the input light. A predetermined change in the resonance shape indicates a presence of the agent in the environment.