A system and method for free space, optical remote sensing of a potential threat agent using spectrally responsive sensor material. In one example the sensor material is formed by particles, which in one particular form are porous photonic crystals. The particles are dispersed into an area being monitored for the presence of the potential threat agent. A pair of lasers is used to generate optical light beams that are directed at the sensor particles after the particles have been dispersed. The light reflected by the sensor particles is then analyzed. The presence of the potential threat agent causes a shift in the spectral peak of light reflected from the sensor particles that can be sensed using photo detectors and a processing subsystem. The system can be tuned to remotely detect for specific chemical, biological or environmental agents that may be present within a given area.