Trace detection of explosives using a membrane-based displacement immunoassay

A compact membrane-based displacement immunoassay has been designed for rap id detection of explosive compounds 2,4,6-trinitrotoluene (TNT) and hexahyd ro-1,3,5-trinitro-1,3,5-triazine (RDX) at high femtomole levels. The system consists of activated porous membranes, onto which either TNT or RDX antib odies are immobilized, that are inserted into microreactor columns, incorpo rated into a flow system. The assay is prepared by saturating the immobiliz ed antibody binding sites with labeled antigen. Target analyte is introduce d upstream of the microreactor, while the displacement of labeled antigen i s monitored downstream using a fluorometer. The concentration of displaced labeled antigen detected is proportional to the concentration of the target analyte introduced into the system. This system provides a reusable and re agentless sensor, suitable for continuous monitoring of explosives, with an operating lifetime of over 50 positive samples. Multiple assays were perfo rmed in approximately 5 min at different flow rates, using membranes satura ted with varying antibody concentrations. The membrane-based format exhibit ed a detection limit of approximately 450 fmol for TNT and RDX (100 mul of 1 ng/ml solution) in laboratory samples. (C) 2000 Elsevier Science B.V. All rights reserved.