Photonic sensors for explosive detection

A microring resonator is used as a photonic sensor device for the detection of the explosive trinitrotoluene (TNT). Selectivity is achieved by coating the sensor chip with specially designed receptor molecules. The measurand is the shift in resonance frequency of the microring resonator induced by the change in effective index of refraction of the waveguide materials due to adsorption/intercalation of the analyte. The response is linear with concentration and reversible, i.e. the TNT molecules desorb from the sensor surface when it is flushed with carrier gas. This enables online measurements since the sensor can be used again after flushing and no sampling is needed. Insensitivity to other substances is demonstrated. Some chemically similar molecules induce a shift also, but the sensitivity is much lower. The sensing limit for TNT is determined to be 0.5ppb. Simultaneous operation of two ring resonators is demonstrated, proving the capability of a multi species monitor ing when the rings are coated with different receptor molecules