Nanoporous organosilicas as preconcentration materials for the electrochemical detection of trinitrotoluene.

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.

Detection of organics using porphyrin embedded nanoporous organosilicas.

Molecularly imprinted polymers and silica have been studied as receptor binding site mimics for use in a wide range of separation, catalysis, and detection applications employing transduction mechanisms including conductometric, amperometric, and capacitance. Porphyrins are also well known as sensor components due to the extreme sensitivity of their spectrophotometric characteristics to changes in their immediate environment. We have developed periodic mesoporous organosilicas (PMO) which incorporate a porphyrin into the material for use as an optical indicator of target binding. This material combines the stability, selectivity, and high density of binding sites characteristic of the molecularly imprinted PMO with the sensitivity and selectivity of the porphyrin. We demonstrate binding of p-nitrophenol, p-cresol, 2,4,6-trinitrotoluene, and RDX by the porphyrin-embedded PMOs with selective adsorption of TNT over the other analytes. In addition, the binding of each of the organics by the PMO results in unique changes in the spectrophotometric characteristics of the incorporated porphyrin. These changes can be observed by visual inspection or through the use of fluorescence spectra collected in 96-well format.

Investigation of surface interactions in molecular recognition of phosphonate imprinted organosilicates and the role of water.

Surface interactions in molecular recognition of phosphonate imprinted organosilicates and the role of water have been studied. NMR and calorimetry studies have shown the changing nature of the surface water structure on silicate surfaces due to template directed molecular imprinting. Results indicate the interaction of an organophosphonate compound with the functionalized silica surfaces to be through surrounding water molecules. However, with nonfunctionalized surfaces, additional higher energy interactions were possible. Further, our results support the possible templating effect of water during the imprint process.

TNT detection using multiplexed liquid array displacement immunoassays.

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.

Prevention of nonspecific bacterial cell adhesion in immunoassays by use of cranberry juice.

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.

Organosilica copolymers for the adsorption and separation of multiple pollutants.

Benzene, diethylbenzene, and ethylenediamine-bridged bistrialkoxy precursors were used in the synthesis of multifunctional PMO copolymers for the adsorption of phenols and metal ions. Polyoxyethylene(10) stearyl ether (Brij 76) was used as the structure director with the surfactant template approach in the synthesis. The resulting PMO copolymers with two or more bridging groups have been characterized by nitrogen gas adsorption, powder X-ray diffraction, and 13C and 29Si solid-state NMR. These organosilicas exhibit large surface areas, narrow pore size distributions, large total pore volumes, and pore ordering consistent with well ordered, hexagonally packed p6mm structures. Minimal competitive effects were observed on the adsorption of p-chlorophenol to the copolymers in the presence of copper ions in solution. Similarly, the presence of p-chlorophenol in solution or adsorbed onto the copolymers did not interfere with copper adsorption. Replacement of a small portion of the benzene bridge in the 90:10 BENZ:EDA copolymer with diethylbenzene produced a copolymer 2.5-fold more efficient for p-chlorophenol adsorption. ICP analysis revealed that greater than 98% of adsorbed copper was removed during extraction with HCl, and this extraction process can be repeated with no difference in copper adsorption after regeneration.