Explosives detection in soil using a field-portable continuous flow immunosensor.

A field method for quantitative analysis of explosives in contaminated soil samples is described. The method is based on a displacement immunoassay performed in a commercial instrument, the FAST 2000, engineered by Research International Inc. The method can be used on-site to measure 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) within 5min. For this study, replicate analyses were performed on soil extracts prepared from each field sample as well as appropriate controls, blanks, and laboratory standards. Statistical analyses were done to assess accuracy, bias, and predictability of the method. The results demonstrated that the immunosensor could be used effectively to screen environmental samples for the presence or absence of explosives. In most samples, the method also provided quantitative values that were in good agreement with standard laboratory analyses using HPLC. A limited number of sample matrices interfered with the immunoassay and produced results that varied significantly from the laboratory data. In each case, the compounds causing the problem have been identified and efforts are being made to minimize these matrix interferences in future field evaluations.

Multianalyte detection using a capillary-based flow immunosensor.

A highly sensitive, dual-analyte detection system using capillary-based immunosensors has been designed for explosive detection. This model system consists of two capillaries, one coated with antibodies specific for 2,4,6-trinitrotoluene (TNT) and the other specific for hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) combined into a single device. The fused silica capillaries are prepared by coating anti-TNT and anti-RDX antibodies onto the silanized inner walls using a hetero-bifunctional crosslinker. After immobilization, the antibodies are saturated with a suitable fluorophorelabeled antigen. A "T" connector is used to continuously flow the buffer solution through the individual capillaries. To perform the assay, an aliquot of TNT or RDX or a mixture of the two analytes is injected into the continuous flow stream. In each capillary, the target analyte displaces the fluorophore-labeled antigen from the binding pocket of the antibody. The labeled antigen displaced from either capillary is detected downstream using two portable spectrofluorometers. The limits of detection for TNT and RDX in the multi-analyte formate are 44 fmol (100 microliters of 0.1 ng/ml TNT solution) and 224 fmol (100 microliters of 0.5 ng/ml RDX solution), respectively. The entire assay for both analytes can be performed in less than 3 min.