On-Site Detection of Explosives in Groundwater with a Fiber Optic Biosensor

Abstract

Two primary explosives involved in groundwater contamination, 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), were detected on-site at low ppb levels with a semiautomated fiber optic biosensor. Validation of the Analyte 2000 (manufactured by Research International Inc., Woodinville, WA) for TNT and RDX detection was performed at two Superfund sites, Umatilla Army Depot and Naval Surface Weapons Center Crane. Samples from monitoring wells were split for analysis using the fiber optic biosensor on-site and using U.S. EPA SW-846 Method 8330 (reverse-phase high performance liquid chromatography) in an offsite laboratory. The Analyte 2000, a multifiber probe fluorimeter, was coupled to a fluidics unit for semiautomated operation. The fiber optic biosensor assay is based on a competitive fluorescent immunoassay performed on the silica core of a fiber probe. From these studies, the limit of detection was determined to be 5 μg/L for both TNT and RDX. In addition to the field samples, extensive laboratory analyses were performed to determine cross-reactivity, matrix effects, and false positive/negative rates.

New horizons: Explosive detection in soil extracts with a fiber-optic biosensor

“…The concentration of TNT or RDX in the acetone extract is proportional to the percent inhibition and was determined by comparison of the percent inhibition to standard curves previously reported from spiked concentrations of TNT or RDX into the buffer. 18 For this study a minimum of seven replicates were analyzed for each extract.…”

“…As previously determined, the MDL for RDX and TNT in groundwater/buffer was 0.005 mg/l. 18 A minimum of a 1:20 dilution was always performed to get the proper acetone concentration (5%) in the test sample for the fiber-optic biosensor. Therefore, the RDX and TNT MDLs for soil prior to any extract dilution for a sample is 0.10 mg/l for the fiber-optic biosensor.…”

“…In addition, samples TJ001 and TJ008 contained high levels of HMX, whereas samples TJ009 and TJ010 had detectable levels of TNB. Because HMX and TNB crossreact with the RDX and TNT antibody, respectively, 18 their presence in sufficient quantity will cause a decrease in fluorescence, thereby increasing the determined concentration of RDX or TNT from the fiber optic biosensor. One method for comparing the results in a statistical fashion is relative percentage difference (RPD) [Eq.…”

“…One such biosensor is the fiber-optic biosensor developed at NRL, originally for the detection of TNT and RDX in ground water. [13][14][15][16][17][18] This sensor uses a competitive fluoroimmunoassay performed on the surface of an optical fiber. In the presence of TNT or RDX, a decrease in the maximum fluorescence (determined by reference/control sample) is observed that is proportional to the concentration of the explosive.…”

Fiber-optic biosensors – an overview

“…(D) Sandwich assay (for explanation see text) Food analysis Competitive FITC-labeled antigens [120] or planar optical waveguides) make use of fluorescencelabeled molecules that can re-emit the absorbed evanescent photons at a longer wavelength by total internal reflection fluorescence (TIRF), as was pointed out in the section on the fundamentals of fiber optics. A portable multichannel fiber-optic immunosensor for on-site detection of the explosives 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) has been optimized on the basis of this sensing scheme 92,93,94], [95. The antibodies are covalently immobilized on the surface of an optical fiber by conventional covalent-coupling techniques. Competition between both TNT or RDX and their labeled analogues Cy5-EDA-(TNB or RDH) for the immobilized antibodies is used as the basis for the detection.…”