TNT sensor

Fig. 37 (a) QD-based sensing of cocaine by the formation of a cocaine-aptamer supramolecular structure that triggers FRET and (b) time-dependent luminescence spectra of the system in the presence of cocaine. The inset shows a calibration curve for variable concentrations of cocaine and a fixed so observation time of 15 min. (c) Schematic of the FRET-based TNT sensor and (d) increase of the QD luminescence upon addition of TNT in the competitive assay format. (Reprinted with permission from [220, 221], Copyright 2009 Royal Society of Chemistry and 2005 American Chemical Society)... 

Goldman ER, Medintz IL, Whitley JL et al (2005) A hybrid quantum dot-antibody fragment fluorescence resonance energy transfer-based TNT sensor. J Am Chem Soc 127 6744-6751... 

Goldman, E. R., I. L. Medintz, J. L. Whitley, A. Hayhurst, A. R. Clapp, H. T. Uyeda, J. R. Deschamps, M. E. Lassman, and H. Mattoussi. A hybrid quantum dot-antibody fragment fluorescence resonance energy transfer-based TNT sensor. J. Am. Chem. Soc. 127, 6744-6751 (2005b). 

The electrochemical TNT sensor was mounted onto the UUV as a separate module, and it serially sent data values to the REMUS UUV. The electrode assembly was mounted on the cone nose of the vehicle and connected to the internal microanalyzer (Fig. 7). Major attention was given to the optimization of variables of the square-wave waveform (including the frequency, amplitude, and potential step) essential for attaining high speed... 

The Office of Naval Research (ONR) conducted the Chemical Sensing in the Marine Environment (CSME) Program to provide a new tool for detecting underwater UXO. Over the last few years, a number of TNT sensors have been developed and evaluated. 

Riskin M., Tel-Vered R., Bourenko T., Granot E., and Willner I., Imprinting of molecular recognition sites through electropolymerization of functionalized An nanoparticles development of an electrochemical TNT sensor based on pi-donor-acceptor interactions, J. Am. Chem. Soc., 130(30), 9726-9733, 2008. 

Fe ) has also been shown to remove As(III) from contaminated soils (15,16), and assist in the remediation of aquifers contaminated with polycyclic aromatic hydrocarbons (26). Other nanomaterials have been developed to act as pollutant sensors, such as the trinitrotoluene (TNT) sensor, which can detect TNT at concentrations as low as 20ng/mL(27). 

An important demonstrated application of this artificial nose system is the high-speed detection of low levels of explosives and explosive-like vapors. Several sensors, based on Nile Red attached to silica microspheres, show high sensitivity to nitroaromatic compounds (NAC) within a mixture12. Different fluorescence response profiles were observed for several NAC s, such as 1,3,5-trinitrotoluene (TNT) and 1,3-dinitrobenzene (DNB), despite their similar structures. These responses were monitored at low concentrations of the NAC vapors (ca. 5 ppb) and at short vapor exposure... 

Figure 7. Simultaneously monitoring vapor signatures of 1000 sensors for 2,4-DNT, 1,3-DNB, and TNT vapor strips at 8% saturated vapor levels. The (noisy) responses for 250 individual sensors are compared to the averaged response profile for 1000 individual sensors. Reprinted with permission from ref. 12a. Copyright 2000 American Chemical Society.

Toal SJ, Magde D, Trogler WC (2005) Luminescent oligo(tetraphenyl)silole nanoparticles as chemical sensors for aqueous TNT. Chem Commun 43 5465-5467... 

Designing a conjugated polymer sensor based on FQ, however, is not only a matter of making a fluorescent polymer for which the photoinduced electron transfer reaction is energetically favorable. There are other important factors that must be considered and requirements that must be met to rehably detect any analyte of interest, including TNT, from the vapor phase. In the broadest sense, these considerations distill to the two primary considerations for any sensing system, sensitivity and selectivity. 

Therefore, there are many considerations that must be taken into account in the design and synthesis of conjugated polymer sensors for explosive detection. Not only must the electron transfer process be efficient, but solid-state aggregation must also be avoided to retain maximum sensitivity. Strong binding of analyte to the polymer is necessary, which the 7l-acidic nature of TNT and DNT facilitate via... 

The selectivity inherent to TNT detection by amplified fluorescent polymers, as described in Section 4, helps to rriinirriize false-positives in land mine detection. These sensor devices respond only to nitroaromatics and similarly small, electron-deficient analytes, which are found typically only in or close to explosives and explosive devices. Field-tests to date have demonstrated that these devices are at least as reliable as trained dogs in detecting explosives that contain nitroaromatics. There is still uncertainty concerning what chemical that dogs actually detect when searching for explosives [17]. This... 

Figure 13 Differential Responses of TNT and DNT, and a volatile interferent, in a dual- channel Fido sensor based on AFP technology. Figure courtesy of ICxTechnologies.

This concept is in essence a chromatographic effect similar to that observed in gas chromatography (GC), with the conjugated polymer film acting as the stationary phase. It is possible that like in GC and other candidate technologies for explosive detection, these responses could be empirically standardized for expected analytes of interest and sensory devices caHbrated to deconvolute temporal quenching signals to determine which analytes are present. This would further enhance the selectivity of what is already a very selective sensor for TNT and related compounds. 

During World War II, copious quantities of ordnance were lost into the harbor at Halifax, Nova Scotia. Decades later, these UUXO now present a significant environmental contamination problem. Studies conducted on this ordnance by Sandia National Laboratories [1] suggest that there may be sufficient concentrations of explosive chemical signature compounds emanating from UUXO to enable detection with chemical sensors. Some UUXO in Halifax Harbor have been shown to produce parts-per-billion levels of explosives in the water near the ordnance. In addition to the parent explosive compound (TNT), other explosive-related compounds such as 2,4-dinitrotoluene (2,4-DNT) were detected, as were degradation products of TNT such as 4-amino-2,6-dinitrotoluene (4-ADNT), and... 

The SeaDog sensor utilized in this work is capable of near real-time detection of low concentrations of explosives in water. The sensor utilizes novel sensing materials originally developed by collaborators at MIT. These materials are fluorescent polymers that are highly emissive when deployed as solid-state thin films. When the polymers interact with nitroaromatic explosives such as TNT, the fluorescence is quenched [3-5], The response of these materials to target analytes... 

The underwater sensor platform is derived from the Fido explosives vapor sensor, originally developed under the Defense Advanced Research Projects Agency (DARPA) Dog s Nose Program. The vapor sensor, whose operation is discussed in Chapters 7 and 9 and in other publications [7-9], was developed for the task of landmine detection. The underwater adaptation of the sensor is very similar to the vapor sensor. In the underwater implementation of the sensor, thin films of polymers are deposited onto glass or sapphire substrates. The emission intensity of these films is monitored as water (rather than air) flows past the substrate. If the concentration of TNT in the water beings to rise, the polymer will exhibit a measurable reduction in fluorescence intensity. The reduction in emission intensity is proportional to the concentration of target analyte in the water. Because the sensor is small, lightweight, and consumes little power, it proved to be ideal for deployment on autonomous platforms. 

On the final day of testing a TNT demolition charge was substituted for the test target constructed from the TNT simulant. The block of explosive was prepared in a manner consistent with how the block would normally be deployed for use. The block was then deployed from the post as previously described. The sensor was positioned at the downcurrent side of the post at a distance of approximately 3 ft. The sensor immediately indicated a strong response to the explosive. 

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