| Quantum dots（QDs） as a kind of zero-dimension nanocrystal have attracted extensive attention in the scientific community due to their unique optoelectronic properties. In particular, QDs are widely used as chemical sensor for the detection of analytes, and the fluorescence methods based QDs have appeared as satisfactory techniques due to their low cost, rapid response, high sensitivity, and low detection limit. However, traditional fluorescent detection often faces with the influence of the coexisting substances, especially those materials which have similar structure and performance. Therefore, the selectivity of QDs needs to be improved and the new construction methods need to be developed.Molecular imprinting, as a powerful and well-established technique, is widely used for synthesizing molecularly imprinted polymers（MIPs） with specific recognition sites. MIPs have many advantages, such as satisfactory practicability, desired predetermination, good stability, and specific selectivity. And the target subjects can easily and selectively rebind into MIPs via specific interactions with the imprinted sites. Hence, it is reasonable to believe that molecular imprinting technique will be a powerful tool to improve the selectivity of the optical detection, and the novel composite material will integrate the merits of high selectivity of MIPs and fluorescence property of QDs. To date, the synthetic methods and detect techniques about the MIPs-based QDs are few. Therefore, novel strategies and methods for fabricating high-performance MIPs fluorescent sensors and the new detection methods are required.In this paper, the aqueous CdTe QDs were adopted as the fluorescent material and the impriting support. Then the silica-based MIPs-CdTe QDs fluorescence sensors（CdTe@SiO2@MIPs）, the surfactant-modified MIPs-CdTe QDs fluorescence sensors（MIPs-OVDAC/QDs） and dual-emission QDs ratiometric fluorescence molecularly imprinted sensors（MIPs-g/r-QDs） were prepared by the molecular imprinting technology incorporating with the sol-gel technology, reverse microemulsion technology, precipitation polymerization technology, swelling technology and surface graft copolymerization technology, respectively. By various of analytical measurements, the morphology, sturcture, chemical composition and optical performance of as-prepared composite fluorescence sensors were investigated. Through the fluorescent recognition experiment, their behaviors of optical detection of the target molecules were studied, and the selective recognition mechanisms were discussed in detail.The main study results of this thesis are as follows:1. The preparation of the silica-based MIPs-CdTe QDs fluorescence sensors（CdTe@SiO2@MIPs） and research of its selective recognition and fluorescence detection performance（1） The CdTe@SiO2@MIPs were synthesized using（thioglycolic acid） TGA capped CdTe QDs as the support, aspirin as the template molecule, 3-aminopropyltriethoxysilane（APTES） as the functional monomer and tetraethoxysilane（TEOS） as the cross-linker via a sol-gel process with surface imprinting. The influence of different parameters on the morphology was also studied. The morpholopy, composition, and optical property of the CdTe@SiO2@MIPs were characterized by TEM, FT-IR and fluorescence spectrophotometer. The spectrofluorometer was used to evaluate the optical stability, effect of pH and detection time, and the optimal detection condition was determined. Under the optimal condition, the fluorescence intensity of CdTe@SiO2@MIPs decreased linearly with the increasing concentration of aspirin in the range of 2.0-50 μmol/L with a detection limit of 0.25 μmol/L. The developed method was successfully applied for the determination of trace aspirin in real biological fluid samples. The excellent performance of CdTe@SiO2@MIPs will accelerate future development of rapid, simple and high efficiency detection of aspirin. The selective recognition results suggested that aspirin caused a significant change of fluorescence intensity with a high quenching amount and MIPs were specific to aspirin but nonspecific to other drugs. The phenomenon can be explained as follows: In the process of the synthesis of CdTe@SiO2@MIPs, many specific recognition sites with respect to the template aspirin were generated on the surface of CdTe@SiO2@MIPs, and the template could be bound strongly to the particles and cause changes in the fluorescence intensity. In addition, the method was successfully applied to the determination of aspirin in human urine and saliva.（2） The CdTe@SiO2@MIPs were synthesized using mercaptosuccinic acid（MSA） capped CdTe QDs as the support, APTES as the functional monomer, TEOS as the cross-linker, and λ-cyhalothrin（LC） as the template molecule by a reverse microemulsion method. The morphology, structure and optical property of CdTe@SiO2@MIPs were characterized by TEM, SEM, FT-IR and fluorescence spectrophotometer. The fluorescence detection experiment shows that LC could cause a significant change of the fluorescence intensity of CdTe@SiO2@MIPs and the linear range of 5.0-60 μmol/L was obtained. The selective recognition experiment shows that CdTe@SiO2@MIPs were specific to LC but nonspecific to other pyrethroids. Finally, the developed method was applicable to routine trace determination of LC in real examples.2. The preparation of the surfactant-modified MIPs-CdTe QDs fluorescence sensors（MIPs-OVDAC/QDs） and research of its selective recognition and fluorescence detection performance（1） The aqueous CdTe QDs with excellent fluorescent property were transferred to organic solvent by using octadecyl-4-vinylbenzyl-dimethyl-ammonium chloride（OVDAC） as a surfactant. Then the MIPs-OVDAC/QDs were synthesized via precipitation polymerization based on OVDAC modified CdTe QDs with acrylamide（AM） as the functional monomer, ethylene glycol dimethacrylate（EGDMA） as the cross-linker, and LC as the template molecule, respectively. The morphology, structure and optical property of the MIPs-OVDAC/QDs were characterized by TEM, FT-IR and fluorescence spectrophotometer. The study also found that different reaction parameters could affect the morphology of the composite fluorescence sensor. Under optimum conditions, the fluorescence detection experiment shows that LC could quench the fluorescence intensity of the MIPs-OVDAC/QDs, and a linear relationship was obtained covering the linear range of 0.1-16 μmol/L with a correlation coefficient of 0.9989 and a high imprinting factor about 5.99. The selective experiment suggests that MIPs-OVDAC/QDs were specific to LC but nonspecific to other pyrethroids. Moreover, the developed method was applicable to routine trace determination of LC in real examples.（2） CdTe QDs were modified by a polymerizable surfactant OVDAC. Subsequently, the OVDAC modified CdTe QDs, bifenthrin（BI, template molecule）, and polystyrene（PS） microspheres were dispersed in chloroform and then transferred into an oil-in-water microcapsule via sonication. Then MIPs-OVDAC/QDs were prepared via a facile and versatile swelling encapsulation strategy. The morpholopy and optical property of MIPs-OVDAC/QDs were characterized by TEM and fluorescence spectrophotometer. Meanwhile, the interactions between BI, QDs and PS were studied by ultraviolet spectra and FT-IR. The study found that the noncovalent interactions（van der Waals and hydrophobic force） made the template molecules fixed in the polymer matrixes. As a result, the fluorescence intensity of the MIPs-OVDAC/QDs was strongly decreased within less than 25 min upon binding BI, and the quenching fractions of MIPs-OVDAC/QDs presented a good linearity with BI concentrations in the range of 0.5-40 μmol/L with a correlation coefficient of 0.9918. In addition, the limit of detection was as low as 0.08 μmol/L, and a high imprinting factor of 4.11 was obtained. The selective experiment shows that MIPs-OVDAC/QDs were specific to BI but nonspecific to other pyrethroids. Furthermore, the developed method was successfully applied to the determination of BI in honey samples. Compared with other fluorescence MIPs, it has three significant differences: firstly, PS microspheres were the polymer matrix and prepared in advance; secondly, the interaction was not hydrogen bond and covalent interaction but van der Waals and hydrophobic force; thirdly, aqueous QDs were successful applied to the swelling process by using a polymerizable surfactant.3. The preparation of dual-emission QDs ratiometric fluorescence molecularly imprinted sensors（MIPs-g/r-QDs） and research of its selective fluorescent recognition and visual detection performance（1） The red-emitting CdTe QDs（r-QDs） were entrapped in the silica nanospheres by a modified reverse microemulsion method to get the r-QDs@SiO2 nanoparticles. And the surface of r-QDs@SiO2 nanoparticles was endowed with reactive vinyl groups through modification with 3-（methacryloyloxy）propyl trimethoxysilane（KH-570）. Then the MIPs-g/r-QDs were prepared by precipitation polymerization method based on r-QDs@SiO2 with OVDAC modified green-emitting CdTe QDs（g-QDs） as the auxiliary fluorescent monomer, tetracycline（TC） as the template molecule, AM as the functional monomer, and EGDMA as the cross-linker, respectively. The optical property, morphology, and structure of MIPs-g/r-QDs were characterized by fluorescence spectrophotometer, TEM and FT-IR. The fluorescent recognition and visual detection experiment shows that MIPs-g/r-QDs had high selective and high sensitivity for the detection of TC. After the experimental conditions were optimized, a linear relationship was obtained covering the linear range of 10-160 μmol/L with a detection limit of 0.35 μmol/L. The selective recognition and visual detection mechanism was discussed in detail. When TC was added into the test solution, the fluorescence of the embedded r-QDs stayed constant, the specific recognition sites could be bound with TC, leading to fluorescence of the OVDAC modified g-QDs in the polymer layer selectively quenched and resulting in fluorescence color changes（from green to red） of the test solution.（2） The dual-emission QDs ratiometric fluorescence glucose imprinted sensor（MIPs-g/r-QDs） were synthsized via surface graft copolymerization. The KH-570 modified r-QDs@SiO2, OVDAC modified g-QDs, glucose, 4-vinylphenylbronic acid（VPBA）, N,N’-methylenebisacrylamide（MBAAm） were used as the supprot, auxiliary fluorescent monomer, template molecule, funtional monomer, cross-linker, respectively. The morphology, structure, and fluorescence property of MIPs-g/r-QDs were characterized by TEM, FT-IR and fluorescence spectrophotometer. The fluorescent recognition and visual detection experiment indicates the fluorescence and visual detectability of MIPs-g/r-QDs for glucose under the optimum conditions. And a linear relationship was obtained covering the linear range of 0.05-1.6 mmol/L with a detection limit of 1.75 μmol/L. The selective recognition experiment shows that MIPs-g/r-QDs had specific recognition and visual detection ability for glucose. The recognition mechanism was also revealed in detail. The fluorescence of the embedded r-QDs stays constant, whereas the functional monomer（VPBA） can selectively bind glucose by the chemistry of boronic acid and cis diol compounds, leading to the fluorescence of g-QDs quenched due to the surface quenching states induced mechanism and resulting in continuous fluorescence color changes of the ratiometric fluorescence sensor system. In addition, the developed ratiometric fluorescence sensor was successfully applied to the detection of glucose in human serum samples.In summary, the MIPs-QDs fluorescence sensors were successfully prepared by combing QDs and MIPs. The morphologies of MIPs-QDs fluorescence sensors were studied, and the problem about the fluorescence quenching of QDs in the polymerization process was neatly solved, and the selective recognition and visual inspection were realized by different interactions, including hydrogen interaction, van der Waals forces and hydrophobic forces, and covalent interactions. The MIPs-QDs fluorescence sensors integrated the merits of the excellent optical property of QDs and high selectivity of MIPs. The combination of the QDs and MIPs provides a new concept and an attractive idea for many fields, such as the preparation of functional materials, fluorescence detection and environmental analysis. Meanwhile, the combination also enriches the preparation of the fluorescent sensors and the applied range of MIPs. |
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