Study On Nanostructured TNT-imprinted Probes And Their Biomimetic Sensitivity Properties

The technique of molecular imprinting creates specific molecular recognition sites in solid materials by using template molecules. The most significant advantages of molecularly imprinted materials are mechanical/chemical stability, low cost and ease of preparation, and hence have attracted extensive research interests due to the potential application in separation, chemical sensors, catalysis, environment detection and drug release etc.This thesis gives a brief overview of the principle of molecular imprinting technique, the novel development of preparation and application of molecularly imprinted polymers, and discusses the problems and challenges that molecular imprinting technique meets with at present. Ideal molecularly imprinted materials should exhibit these characteristic as follow: complete removal template molecules, able to be post-synthetically functionalized, homogeneous imprinted sites of high stability, high affinity, rapid binding kinetics and transduction of binding into easy readout etc. However, traditional molecular imprinting techniques often produce the polymer materials exhibiting high selectivity but low binding capacity, poor site accessibility, and slow binding kinetics due to most imprinted recognition sites to be embedded in high rigid polymer matrix interior. Therefore, controlling template molecules to locate in the proximity of materials surface is critical to create more effective recognition sites and to improve sites accessibility. As an alternative to these approaches, nano-sized imprinting materials may provide a potential solution to these difficulties due to their extremely high surface-to-volume ratio which lead to the recognition sites to locate in the proximity of materials surface. This thesis aims at an exclusive TNT recognition and detection. TNT-imprinted nanospheres, nanowires and nanotubes with high density imprinted sites, high selectivity, high affinity and rapid binding kinetics had been prepared by means of using nanotechnology, surface functionalized design and molecular imprinting technique etc. Moreover, molecular recognition properties and sensitivity mechanism of nanostructured molecularly imprinted materials to trace TNT molecular were also investigated.Molecularly imprinted spherical polymers for explosive TNT detection were prepared by a one-step precipitation polymerization procedure. The polymer particles exhibited a regular shape in the nano-scale range. Moreover, the size and the uniformity of the particles were influenced by types and concentrations of monomers, polymerization temperature, and the concentration of initiator. The binding test indicated that the nano-spherical imprinted polymers possessed higher specific affinity and faster binding kinetics to TNT templates in comparison with traditional imprinted polymers prepared by bulk polymerization. Two classes of specific binding sites in the polymer matrix were investigated by Scatchard analysis, which indicated that two kinds of complexes between functional monomers and templates were formed before the polymerization process. Comparing with the structure of TNT and acrylamide, one kind of complex between TNT and acrylamide was strongly charge-transfer complexing interaction by p-Ï€complex between electron-rich amino group of acrylamide and electron-deficiecy-benzene ring of TNT, the other was hydrogen bonding interaction between amino group (-NH₂) of acrylamide molecule nitro group (-NO₂) of TNT.A surface molecular self-assembly strategy for molecular imprinting of polymer nanowire/nanotube arrays in alumina membrane was reported. The imprinting strategy is based on the findings that TNT template molecules can spontaneously assemble onto 3-aminopropyltriethoxysilane (APTS)-modified alumina pore walls by a strong charge-transfer complexing interaction between amino groups and electron-deficient nitroaromatics instead of using chemical immobilization of template molecules on surface. In order to further enhance the total recognition sites of TNT in the resultant imprinted nanostructures, an additional amount of TNT templates was replenished to the mixture solution of polymerization precursors for further creating TNT regular interior recognition sites within polymer matrix. A stepwise progressive polymerization was designed toward the controllable preparation of high-quality arrays of TNT-imprinted polymer nanowires and nanotubes in alumina membrane. Compared to traditional imprinted particles, the imprinted nanowires/nanotubes with high density of surface imprinted sites and regular interior sites can significantly improve the binding capacity, binding kinetics and recognizing selectivity.Silica nanotubes are ideal vehicles for imprinting a variety of organic or biological molecules because they are easy to make, have cross-linked rigid structures, are highly suitable for the formation of delicate recognition sites, and because silica surfaces can be modified with an enormous variety of chemically functional groups using simple silane chemistry. In this study, we report a simple procedure for applying a molecular imprinting technique to imprint TNT molecules into the ultra-thin walls of silica nanotubes which were prepared by a sol-gel template-synthesis method. During sol-gel of silica process, APTS-TNT complexes by electron-transfer complexing interaction between the electron-rich amino groups of APTS and the electron-deficient TNT were detained in silica matrix to create TNT recognition sites. On the other hand, TNT templates can spontaneously assemble onto APTS-modified alumina pore walls by strong charge-transfer complexing interactions, which effectively increase the density of TNT imprinted sites in the outer surface of silica nanotubes. Silica sol within the alumina pores had undergone contraction during the drying and calcination processes. In order to prepare high quality silica nanotubes in the alumina pores, a stepwise progressive gel process is designed by controlling aging temperatures. Because at a slower rate of gel, contraction of gel can mainly occur in a direction perpendicular to the alumina pores due to electrostatic interaction and chemical affinities between silica sol-gel and the pore walls of APTS-modified alumina membrane. Moreover, fluorophore (FITC) was embedded into silica nanotubes by a reaction of amino groups (-NH₂) and isothiocyanate groups (-NCS) in order to label of fluorescence to TNT recognition sites. When TNT molecules were selectively adsorbed by TNT-imprinted nanotubes with fluorescence labeling, excitated electrons of fluorophore (FITC) can transfer to electron-deficient TNT molecules, which caused electron-transfer fluorescence quenching. Therefore, sensitivity binding signal between TNT molecules and recognition sites in TNT-imprinted nanotubes was obtained.