Trace level detection of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by microimmunosensor

Reported in this paper is the development and characterization of a highly sensitive microcapillary immunosensor for the detection of the explosive, h exahydro-1,3,5-trinitro-1,3,5-triazine (RDX). The immunosensor exploits ant ibodies as recognition elements for target antigens, fluorescence dye conju gates for reporter molecules and fused silica microcapillaries for its high surface-to-volume ratio. Detection of RDX with the microcapillary immunose nsor requires covalent immobilization of anti-RDX antibodies on the inner c ore of the microcapillaries via heterobifunctional cross-linker chemistry. Subsequent saturation of all antibody binding domains follows with a synthe tically prepared fluorescent analog of RDX. Displacement immunoassays were performed with the microcapillary immunosensor with the injection of unlabe led RDX at concentration levels from 1 part-per-trillion (pptr) to 1000 par t-per-billion (ppb). As unlabeled RDX reaches the binding domain of the ant ibody, fluorescent RDX analog is displaced from the antibody, flows downstr eam and is measured by a spectrofluorometer. Fluorescence measurements of t he displaced fluorescent RDX analog were equated to a standard calibration curve to quantify sample concentration. Complete evaluation of the RDX micr ocapillary immunosensor for selectivity and sensitivity was performed based on the following criteria: variable flow rates, antibody cross-reactivity, reproducibility and cross-linker (carbon spacer) comparison. Results indic ate the lowest detectable limit (LDL) for RDX is 10 pptr (ng/l) with a line ar dynamic range from 0.1 to 1000 ppb (mu g/l). (C) 1999 Elsevier Science S .A. All rights reserved.