| There are many different kinds of explosives in the world, which can be concealed in the packages. The various types of explosives and the different ways explosives can be hidden make identifying the exact location of concealed explosives very difficult. Most explosives contain nitro-aromatic compounds (NACs) as necessary components. NACs refers mainly to 2,4,6-TNT, 2,4-DNT, and PA, etc. Up to now, detection techniques of explosives of all types have already been built for NACs. NACs are not only used in preparation of explosives, but also produced in large quantities for industrial uses in the preparation of drugs, perfumes, and dyes, etc. However, they are toxic and due to their wide use and serious harm, leaching of NACs could be an environmental disaster. The fast and accurate detection of NACs in solution has become increasingly important in terms of anti-terrorism, environmental protection, etc.Currently, various methods such as canines, gas chromatography coupled with mass spectrometry, high-pressure liquid chromatography, surface enhanced Raman spectrometry, electrochemical method and fluorescent sensors have been developed for the detection of NACs in liquid phase. Compared with the above mentioned techniques, fluorescent sensors have gained great attention because of their high sensitivity and selectivity, multiple choices in signals or parameters, and low cost in instrumentation. Clearly, these advantages will benefit on-site analysis.In the first chapter of this dissertation, progress in the studies of various fluorescent sensors, including homogeneous sensors, film sensors, particle sensors and sensors based on the principles of biology, used for the detection of NACs in solution are addressed, and at the same time, the advantages and disadvantages of each type of the sensors are briefly discussed. It is anticipated that creation of new fluorescent film sensors and development of the film-based explosive detectors, which may possess characteristics like high quality, high efficiency, multiple-functionalities and low cost etc., will become one of the hot points in the area of explosive detection studies.Over the past decade, our group has devoted on developing a new family of fluorescent sensing films via a SAM way and has realized sensitive and selective detection of NACs in vapor phase and of other analytes in solution. It is to be noted that the structures of the spacers connecting the sensing elements and the substrates have played important roles in mediating the sensing behaviors of the obtained films. Moreover, in the process of studying low-molecular mass organic gelators, we have found that the introduction of a simple benzene ring in the spacer of two cholesteryl units resulted in a remarkable effect upon their assembling behaviors in solution. Based on the above consideration and the previous work in our group, benzene structure was intentionally introduced into the spacer, and pyrene was chemically immobilized, in a SAMs'way, onto a substrate, a glass plate, surface via the spacer as mentioned. These films show stable fluorescence emission in aqueous phase and are sensitive to the presence of NACs.In the first section of this dissertation, a new fluorescent film was prepared by immobilizing pyrene on an isocyanatopropyl-terminated glass plate surface via a polar linker which contains a benzene structure in a SAMs'way. The fine structure of the film's surface is tunable, and it can be used to detect NACs in aqueous phase. The photophysical studies of this film help us to understand the "two-dimensional solution" model further. Compared with the fluorescent film sensors containing other alkyl chains in the spacer, the present film exhibits not only perfect excimer emission, but also distorted excimer emission in aqueous phase.In the second section of this dissertation, another fluorescent sensing film was fabricated by chemical assembling pyrene moieties on a glass plate surface via a spacer containing a benzene ring and an imino structure. The film was used for the detection of NACs, particularly PA, in aqueous phase. The introduction of benzene ring in the spacer favorsπ-πstacking between pyrene moieties on the end of each spacer, which facilitates direct exposure of the fluorophore residues to aqueous phase, and thus the film is able to quickly monitor NACs. The advantages of this design have been demonstrated experimentally in terms of the highly sensitive response of the above-mentioned film to the presence of trace amounts of NACs in aqueous solution. The detection limit (DL) of the film to PA reaches down to 1.0×10-8mol/L. Further experiments demonstrated that the sensing process is fully reversible and is free of interference from common chemicals'like toluene, benzene, chloroform, ethanol, artificial sea water, NaOH, HC1, etc. Furthermore, fluorescence life time measurements revealed that the quenching is static in nature. |
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