Environmental immunoassay for the explosive RDX using a fluorescent dye-labeled antigen and the continuous-flow immunosensor

To assist in explosives detection for airport security and environmental remediation efforts, a biosensor has been developed at the Naval Research Laboratory based on immunoassays for explosives which are inexpensive, sensitive, and specific for the compound in question. Recently, an analog and antigen-protein complex of the plastic explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) became commercially available. In this report, we present a synthetic scheme for the preparation of a dye-labeled analog of RDX and demonstrate its use in the detection of explosives in environmental samples. The RDX analog is linked to the succinimidyl ester of a sulfoindocyanine dye via two amide bonds using 1,5-diaminopentane. This dye conjugate is then allowed to bind to antibodies against RDX which are immobilized on plastic beads inside a 100 mu l column. Upon injection of samples into the stream of buffer flowing through the column, the fluorescent analog is displaced from the column in amounts which are proportional to the concentration of the analyte. Concentrations of RDX as low as 15 ppb are easily measurable in laboratory samples using this system. The continuous-flow immunosensor is also able to detect quantitatively RDX in environmental samples.