Fluorescence quenching of CdSe quantum dots by nitroaromatic explosives and their relative compounds

CdSe quantum dots (QDs) were synthesized in oleic acid and octadecene medium under high-temperature and dispersed in chloroform. Nitroaromatic explosives and their relative compounds, 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), nitrobenzene (NB), 2,4-dinitrochlorobenzene (DNBCl) and p-nitrotoluene (NT) can obviously cause the fluorescence quenching of the synthesized QDs. Under the optimum conditions, a nonlinear response was observed over the concentration range of 10(-8) to 10(-5) M for them all. The modified Stern-Volmer quenching equations of ln I(0)/I versus C show a good linear relation in 10(-5) M order of magnitude, and the detection limits approach 10(-6) to 10(-7) M.

Biosensor-based on-site explosives detection using aptamers as recognition elements

Reliable observation, detection and characterisation of polluted soil are of major concern in regions with military activities in order to prepare efficient decontamination. Flexible on-site analysis may be facilitated by biosensor devices. With use of fibre-optic evanescent field techniques, it has been shown that immunoaffinity reactions can be used to determine explosives sensitively. Besides antibodies as molecular recognition elements, high-affinity nucleic acids (aptamers) can be employed. Aptamers are synthetically generated and highly efficient binding molecules that can be derived for any ligand, including small organic molecules like drugs, explosives or derivatives thereof. In this paper we describe the development of specific aptamers detecting the explosives molecule TNT. The aptamers are used as a sensitive capture molecule in a fibre-optic biosensor. In addition, through the biosensor measurements the aptamers could be characterised. The advantages of the aptamer biosensor include its robustness, its ability to discriminate between different explosives molecules while being insensitive to other chemical entities in natural soil and its potential to be incorporated into a portable device. Results can be obtained within minutes. The measurement is equally useful for soil that has been contaminated for a long time and for urgent hazardous spills.

Sensors--an effective approach for the detection of explosives

The detection of explosives and explosive related illicit materials is an important area for preventing terrorist activities and for putting a check on their deleterious effects on health. A number of different methods, based on different principles, have been developed in the past for the detection of explosives. Sensors are one of those methods of detection which have capability to mimic the canine system and which are known to be the most reliable method of detection. The objective of this review is to provide comprehensive knowledge and information on the sensors operating on different transduction principles, ranging from electrochemical to immunosensors, being used for the detection of explosives as they pose a threat for both health and security of the nation. The review focuses mainly on the sensors developed in the recent 5 years and is prepared through summary of literature available on the subject.

Development of new rat monoclonal antibodies with different selectivities and sensitivities for 2,4,6-trinitrotoluene (TNT) and other nitroaromatic compounds

Five new rat monoclonal antibodies (mAbs) for 2,4,6-trinitrotoluene (TNT) and other nitroaromatic compounds, including, especially, the metabolite 2-amino-4,6-dinitrotoluene (2-ADNT), are described. Five heterogeneous, competitive enzyme-linked immunosorbent assays (ELISAs) were developed. Assay 1 uses mAb DNT4 3F6 as recognition element and gives a standard curve for TNT in 40 mmol L(-1) phosphate buffered saline (PBS) with a test midpoint (IC50) of 0.26+/-0.08 microg L(-1) (n=20). Assay 2 (mAb DNT4 4G4) has an IC50 of 0.35+/-0.07 microg L(-1) (n=18), assay 3 (mAb DNT4 1A3) has an IC50 of 0.73+/-0.14 microg L(-1) (n=15), and assay 4 (mAb DNT4 1A7) has an IC50 of 2.32+/-0.70 microg L(-1) (n=15). Assay 5 (mAb DNT2 4B4) is very selective for 2-ADNT and has an IC50 of 8.5+/-1.7 microg L(-1) (n=15) in PBS. These antibodies for nitroaromatic compounds differ not only in their sensitivity but also in their selectivity. Major cross-reactants are 1,3,5-trinitrobenzene, 2-ADNT, 4-amino-2,6-dinitrotoluene (4-ADNT), 2,4-dinitroaniline, 3,5-dinitroaniline, and 2,6-dinitroaniline. Although assay 5 is not highly sensitive, the mAb DNT2 4B4 in this assay is highly selective for 2-ADNT. Of all the compounds tested, only 2,4-dinitroaniline and 3,5-dinitroaniline had relevant cross reactivities, 18% and about 26%, respectively. Two ELISAs, using mAbs DNT4 3F6 and DNT2 4B4, were used to analyze different concentrations of TNT and 2-ADNT, respectively, in three different surface water matrices (river and lake water). Both assays were affected by the matrix, but usually performed well (recovery within the range 70-120%). In addition, these ELISAs were used to analyze mixtures of TNT, 2-ADNT, and 4-ADNT, at three different concentrations, in the same water matrices. A different recognition pattern was clearly visible with both assays and depended on the cross reactivities of the corresponding mAb.

Detection of 2,4,6-trinitrotoluene in environmental samples using a homogeneous fluoroimmunoassay

We have tested both soil and water environmental samples for 2,4,6-trinitrotoluene (TNT) using a simple homogeneous assay. This assay is based on changes in fluorescence emission intensity when a fluorescently labeled TNT analogue, bound to an anti-TNT antibody, is competitively displaced by TNT. Fluoroimmunoassay results for TNT concentrations in diluted acetone extracts prepared from archived soils were in good agreement with the results from high-performance liquid chromatography analysis of the same sample extracts. In addition, assays of TNT-spiked environmental well water gave results essentially identical with assays conducted in a TNT-spiked laboratory buffer. The homogeneous fluoroimmunoassay, which is rapid, simple, sensitive, and amenable to high throughput screening, shows promise for near real-time evaluation of TNT contamination in environmental samples.