No abstract

The presence of trace contamination of soil and groundwater with explosives is an ongoing concern, for which improved methods are required to facilitate their detection and quantification. This is true both for the monitoring of remediation and for site characterization. Immunosensors have been found effective for solution-phase detection of environmental contaminants. Our work utilized the Luminex100 (flow cytometer) to detect TNT in a multiplexed displacement immunoassay format. The Luminex100 can perform a multiplexed assay by discriminating between up to 100 different bead sets. We used this capability to evaluate four different TNT monoclonal antibodies, two recombinant TNT antibodies, and a control antibody simultaneously for the rapid detection of TNT and other nitroaromatics. TNT could be detected at 0.1 ppb and quantified over the range of 1.0 ppb to 10 ppm. In addition, the assay was shown to be effective in various matrixes such as lake water, seawater, and acetone extracts of soil. Seawater required dilution with two parts buffer to avoid loss of microspheres, while the acetone extracts were diluted 100-fold or more to minimize solvent affects.

We describe the use of nanoporous organosilicas for rapid preconcentration and extraction of trinitrotoluene (TNT) for electrochemical analysis and demonstrate the effect of template-directed molecular imprinting on TNT adsorption. The relative effects of the benzene (BENZ)- and diethylbenzene (DEB)-bridged organic-inorganic polymers, having narrow or broad pore size distributions, respectively, on electrochemical response and desorption behavior were examined. Sample volumes of 0.5-10 mL containing 5-1000 ppb TNT in a phosphate-buffered saline buffer were preconcentrated in-line before the detector using a microcolumn containing 10 mg of imprinted BENZ or DEB. Square-wave voltammetry was used to detect the first reduction peak of TNT in an electrochemical flow cell using a carbon working electrode and a Ag/AgCl reference electrode. Imprinted BENZ released TNT faster than imprinted DEB with considerably less peak tailing and displayed enhanced sensitivity and an improvement in the limit of detection (LOD) owing to more rapid elution of TNT from that material with increasing signal amplitude. For imprinted BENZ, the slope of signal versus concentration scaled linearly with increasing preconcentration volume, and for preconcentrating 10 mL of sample, the LOD for TNT was estimated to be 5 ppb. Template-directed molecularly imprinted DEB (TDMI-DEB) was 7-fold more efficient in adsorption of TNT from aqueous contaminated soil extract than nonimprinted DEB.

Mercury salts are commonly used in laboratory and field experiments as biocides. It has been previously reported that Hg(II) can enhance chemical hydrolysis of a number of pesticides. Earlier studies on metal-promoted hydrolysis have reported overall rate constants as a function of total metal concentration. There are three advantages in reporting the relative importance of the different species:  (1) results can be extrapolated form one situation to another, (2) rates can be predicted for specific conditions, and (3) greater understanding of the catalysis mechanism can be gained. In this study, mercury-promoted hydrolysis of parathion-methyl (O,O-dimethyl-O-p-nitrophenyl phosphorothionate), a probe organophosphate compound (OP), was studied as a function of Hg(II) speciation. The observed rate of hydrolysis was a function of specific mercury species rather than of the total mercury in solution. Second-order rate constants were determined experimentally at various pH values. A pH-dependent kinetic expression, k obs = (αHg 2+ k 1 + αHgOH + k 2 + αHg(OH) 2 k 3) where ki = with Ki representing the Hg:OP equilibrium constant, the rate constant for Hg:OP hydrolysis for the different Hg(II) species, and α is the fraction of the total Hg(II) present as specific species, provides a plausible interpretation for the system. Mercury-chloride species proved to have little catalytic power, whereas the contributions for Hg2+ and Hg(OH)+ were significant. Our results also suggest that a mixed mechanism (electrophilic and nucleophilic) may have to be considered for general metal-promoted hydrolysis of OPs.

The ability of Vaccinum macrocarpon, the North American cranberry, to prevent bacterial adhesion has been used to advantage in the prevention of urinary tract infections and has recently been described for the prevention of adhesion of bacteria responsible for oral infections and stomach ulcers. This report documents the ability of cranberry juice to reduce nonspecific adhesion of bacteria to the borosilicate glass microscope slides used in an immunoarray biosensor format. Nonspecific binding of analytes in the array sensor leads to high background signals that cause increased detection limits and false positives. Reduction in background-to-signal ratios can be seen as the juice concentration is increased from 0 to 50% of the sample. This impact cannot be duplicated with grape, orange, apple, or white cranberry juice. Sugar content and pH have been eliminated as the agents in the juice responsible for the anti-adhesive activity.