Detection of TNT in Water Using an Evanescent Wave Fiber-Optic Biosensor

A general health hazard from explosive toxicity exists due to poor storage facilities for explosives and from contamination of soil and water with byproducts of explosive manufacture. To provide an effective method for monitoring water contamination, the Naval Research Laboratory's fiber-optic biosensor was adapted for the detection of small molecules such as explosives. A competitive immunoassay was developed for the detection of the most widely used explosive, trinitrotoluene (TNT). Trinitrobenzenesulfonic acid (TNB), an analog of TNT, was labeled with a fluorophore and used as the analyte competitor. A solution containing 7.5 ng/mL sulfoindocyanine 5-ethyl-enediamine-labeled TNB (Cy5-EDA-TNB) was exposed to an antibody-coated optical fiber, generating a specific signal above background that corresponds to the 100% or reference signal. Inhibition of the 100% signal was proportional to the TNT concentration in the sample. Detection sensitivities of 10 ng/mL TNT (8 ppb) in buffer were achieved. Tests on river, harbor, and bilge water samples spiked with TNT showed results similar to tests on laboratory (buffer matrix) samples. To determine possible interferences, several structural analogs ofTNT were tested.