New horizons: Explosive detection in soil extracts with a fiber-optic biosensor

Contamination of soils with the explosives TNT and RDX is a worldwide problem that has resulted from inadequate disposal methods. Many of these contamination sites are currently being characterized or are undergoing remediation. The ability to obtain real-time, on-site results would save remediation time, reduce cost, and provide for efficient use of labor during cleanup. The NRL fiber-optic biosensor, which has been demonstrated for the on-site detection of explosives in ground water, has expanded its horizons to include detection in soil extracts. Soil samples from several sites in the United States were analyzed for TNT and RDX. The explosives were removed from the soil with a 3-min acetone extraction. The extract was mixed with buffer containing a fluorescent explosive analog and exposed to the antibody-coated optical probes. In the presence of either TNT or RDX, a decrease in the fluorescence signal, proportional to the explosive concentration, was observed. In less than 20 min, analysis on four optical probes was completed. Extract results from the fiber-optic biosensor were compared to those from U.S. EPA SW 846 Method 8330 (reverse-phase high-performance chromatography). Detection limits of 0.5 mg/kg (0.1 mg/l) of TNT and RDX in soil acetone extracts were obtained.