High-speed fluorescence detection of explosives-like vapors

In this paper, we report on the preparation of novel crossreactive optical microsensors for high-speed detection of low-level explosives and explosive s-like vapors. Porous silica microspheres with an incorporated environmenta lly sensitive fluorescent dye are employed in high-density sensor arrays to monitor fluorescence changes during nitroaromatic compound (NAC) vapor exp osure. The porous silica-based sensor materials have good adsorption charac teristics, high surface areas, and surface functionality to help maximize a nalyte-dye interactions. These interactions occur immediately upon vapor ex posure, i.e., in less than 200 ms and are monitored with a high-speed charg e-coupled device camera to produce characteristic and reproducible vapor re sponse profiles for individual sensors within an array. Employing thousands of identical microsensors permits sensor responses to be combined, which s ignificantly reduces sensor noise and enhances detection limits. Normalized response profiles for 1,3-dinitrobenzene (1,3-DNB) are independent of anal yte concentration, analyte exposure time, or sensor age for an array of one sensor type. Explosives-like NACs such as 2,4-dinitrotoluene and DNB are d etected at low part-per-billion levels in seconds. Sensor-analyte profiles of some sensor types are more sensitive to low-level NAC vapor even when in a higher organic vapor background. We show that single element arrays perm it the detection of low-level nitroaromatic compound vapors because of sens or-to-sensor reproducibility and signal averaging.