Luminescence-based methods for sensing and detection of explosives.

The detection of explosives and related compounds is important in both forensic and environmental applications. Luminescence-based methods have been widely used for detecting explosives and their degradation products in complex matrices. Direct detection methods utilize the inherent fluorescence of explosive molecules or the luminescence generated from chemical reactions. Direct detection methods include high-energy excitation techniques such as gamma-ray and x-ray fluorescence, detection of decomposition products by fluorescence or chemiluminescence, and detection following reduction to amines or another reaction to produce fluorescent products from the explosive. Indirect detection methods utilize the interference caused by the presence of explosive compounds with traditional processes of fluorescence and fluorescence quenching. Indirect detection methods include quenching of solution-phase, immobilized, and solid-state fluorophores, displacement of fluorophores, fluorescence immunoassay, and reactions that produce fluorescent products other than the explosive. A comprehensive review of these methods is presented.

Investigation of common fluorophores for the detection of nitrated explosives by fluorescence quenching.

Previous studies have indicated that nitrated explosives may be detected by fluorescence quenching of pyrene and related compounds. The use of pyrene, however, invokes numerous health and waste disposal hazards. In the present study, ten safer fluorophores are identified for quenching detection of target nitrated compounds. Initially, Stern-Volmer constants are measured for each fluorophore with nitrobenzene and 4-nitrotoluene to determine the sensitivity of the quenching interaction. For quenching constants greater than 50 M(-1), sensitivity and selectivity are investigated further using an extended set of target quenchers. Nitromethane, nitrobenzene, 4-nitrotoluene, and 2,6-dinitrotoluene are chosen to represent nitrated explosives and their degradation products; aniline, benzoic acid, and phenol are chosen to represent potential interfering compounds. Among the fluorophores investigated, purpurin, malachite green, and phenol red demonstrate the greatest sensitivity and selectivity for nitrated compounds. Correlation of the quenching rate constants for these fluorophores to Rehm-Weller theory suggests an electron-transfer quenching mechanism. As a result of the large quenching constants, purpurin, malachite green, and phenol red are the most promising for future detection of nitrated explosives via fluorescence quenching.