【作者】 王建浩；

【导师】 赵元弟；

【作者基本信息】 华中科技大学 ， 生物医学工程， 2009， 博士

【摘要】 作为一种新型荧光材料，量子点(Quantum Dots，QDs)具有很多优异的性质，如激发谱宽、发射谱窄而对称、斯托克斯位移(Stoke’s shift)大、抗光漂白和荧光寿命长等优点，在生命科学领域显示了极其广阔的应用前景。尽管量子点在生物医学尤其是生物荧光标记中得到广泛的研究和应用，但还有很多有待解决的问题：如何发展和完善量子点的合成方法，提高量子点的稳定性及生物相容性，以及怎样采取更好的方法解决量子点与生物分子偶联，如何将偶联物进行分离提纯形成特异性、稳定的探针等等。目前生物学上应用的量子点大多来自有机相合成，该方法合成的量子点粒径分布均匀，量子产率高，但制备条件苛刻、成本高、毒性大。相比之下，水相合成方法简单、毒性小、成本低、重复性好，并且水相合成的量子点可以直接与生物分子偶联，因而具有非常广阔的应用前景。本论文主要工作以不同的巯基小分子作为稳定剂合成高质量的水溶性CdTe量子点，同时也研究了其光学、表面化学和生物偶联等特性，并重点研究了合成的量子点作为荧光探针在生物和分析领域的具体应用。论文完成的工作如下：(1)采用多种巯基小分子做稳定剂，水相合成性能优异的CdTe量子点。通过控制加热回流时间，可得到发射波长在510～660 nm之间的量子点，并对合成的水溶性量子点进行荧光发射光谱、紫外可见吸收光谱、透射电子显微镜成像、X射线粉末衍射、X射线荧光光谱和红外光谱等系列表征。(2)采用水相合成法制备以巯基丙酸为稳定剂的水溶性CdTe量子点，并利用变性BSA(dBSA)修饰CdTe量子点，实验表明dBSA可以有效地连接到QDs上，并且这种连接非常稳定。通过葡聚糖凝胶层析确定QDs与dBSA连接的最佳比例，并分离提纯得到dBSA-QDs。进一步实验表明，通过这种方式得到的dBSA-QDs，不仅其量子产率可以大大提高，而且其抗光漂白性和稳定性也有大幅提高。利用提纯后的dBSA-QDs为探针，基于荧光淬灭的原理对Ag~+进行了检测。结果表明，其对Ag~+检测的线性范围为0．08-10．66μM，检测下限为0．01μM。该方法为金属离子的检测提供了一条新的思路。(3)研究了CdTe量子点的温度敏感性并建立了一种提高量子点荧光的温度稳定性的方法。发现巯基丙酸为稳定剂的水溶性CdTe量子点(直径约3．5 nrn)的荧光对温度非常敏感，随着温度从278 K升高到323 K，其荧光强度降为原来的50．2％，且其荧光发射峰位置也发生明显红移(～7 nn)。而其表面修饰变性卵清蛋白之后，其对温度的不敏感性大大提高，荧光强度可以保持70％以上，而且荧光发射峰位置只有约2 nm的红移，并且经过多次升温、降温之后，其荧光强度和波长都可以恢复。这一结果为寻找具有温度稳定性的量子点荧光探针提供了重要依据。(4)基于CdTe量子点荧光光谱的变化建立了一种可用于卵清蛋白检测的新方法。用变性卵清蛋白修饰CdTe量子点后，发现CdTe量子点的荧光强度和发射峰波长都发生明显变化，建立了一种用CdTe做荧光探针定量检测卵清蛋白的新方法。实验结果表明，在优化条件下，在0．125μM-4μM范围内，体系的荧光强度和最大发射峰波长的变化均与卵清蛋白的浓度呈良好的线性关系，检测限达到0．03μM。紫外吸收法证实，此方法具有很好的准确性。(5)以巯基丁二酸为稳定剂，制备了核壳型的CdTe／CdS量子点，紫外吸收光谱和荧光光谱证实所合成的量子点具有良好的光学性质。又发现通过升温、降温处理的方式，可以大大提高该量子点的量子产率(达到41％)。之后又将这种高性能的量子点用于制备荧光探针。实验结果表明，转铁蛋白可以有效地连接到CdTe／CdS量子点上，并基于转铁蛋白受体识别介导作用实现对人肝癌细胞HepG2的识别。这一工作对于制备高性能的量子点，促进其在生命科学中的应用具有重要意义，同时也对肿瘤细胞的识别诊断研究具有参考价值。(6)以谷胱甘肽为稳定剂，在水相中合成了高质量的CdTe量子点，紫外吸收光谱和荧光光谱证实所合成的量子点具有良好的光学性质。通过毛细管电泳技术比较戊二醛两步法和戊二醛一步法对伴刀豆球蛋白的标记效果，实验结果表明，戊二醛两步法具有更好的标记效果。更多还原

【Abstract】 As a new type of fluorescent labels,quantum dots (QDs)offer a number of attractivefeatures,including broad excitation spectra,relatively broad and symmetric luminescencebands,large Stokes shift,high photobleaching threshold,good chemical stability and longfluorescence lifetime,which make them have broad protenal application in life science.Even though QDs have been widely used in biomedical,especially in the biologicalfluorescent labeling,but still have a lot of problems to be resolved:How to develop andimprove the QDs synthesis methods,the stability and biocompatibility,as well as how totake better ways to solve QDs coujugated with biological molecules,and how to separateand purify of the conjugates to get stable bioprobes,and so on.At present,most of thebiological applications of QDs come from the organic-phase synthesis,and QDssynthesized in this method have good size distribution and high quantum yield.But thismethod is hard to operate,high cost and toxic.In contrast,water-phase synthesis methodis simple,small toxicity,low cost and good reproducibility,etc.Water-phase synthesis ofQDs can be conjugated directly with biological molecules,which have very broadapplication prospects.The main job of this thesis is to synthesize high-qualitywater-soluble CdTe QDs with different small sulfhydryl molecule as the stabilizer,andalso conduct a study of its optical,surface chemical and bioconjugated properties,andfocused on the specific applications of the as-synthesized QDs as fluorescent labels in thefield of biology and analysis.The main contents and results are summarized as follows:(1)Water-soluble CdTe QDs were synthesized in aqueous solution by using differentsmall sulfhydryl molecules as the stabilizer.The fluorescence emission peaks at 510～660nm are tuned by the control of the refluxing time.The as-synthesized quantum dots werethen characterized by fluorescence spectroscopy,UV-visible spectroscopy,TEM,XRD,EDXS and infrared spectroscopy,respectively.(2)CdTe QDs were synthesized in aqueous solution with 3-Mercaptopropionic acid(MPA)as the stabilizer.Denatured bovine serum albumin (dBSA)has been used tomodify the surface of QDs.Experiment results showed that the dBSA could be effectivelyconjugated to the surface of CdTe QDs.Column chromatography was used to purify the conjugates and determine the optimum conjugate ratio of dBSA to QDs.Furtherexperiment results showed that the dBSA after conjugated to QDs efficiently improve thephotoluminescence quantum yield (PL QY),the chemical stability and the stability againstphotobleaching.A facile and sensitive method for silver (I)ions determination wasproposed based on the fluorescence quenching of the dBSA-QDs.Under the optimumconditions,the relative PL intensity decreased linearly with the silver (I)ions’concentration in the range of 0.08 to 10.66μM.The detection limit was 0.01μM.Thisstudy provides a new trail of thought for the detection of metal cations.(3)The temperature-dependent of CdTe was studied and a method of improving thetemperature-insensitive was established.The PL of CdTe QDs (3.5 nm)is found to betemperature-dependent:as the temperature arising from 278 K to 323 K,the PL intensitydeclines to 50.2% of its original and PL emission peak shows obvious red-shift (～7 nm).After modification of the QDs surface with denatured ovalbumin,the PL is moretemperature-insensitive than before.The PL intensity retains more than 70% of its originaland the emission peak shows less red-shift (～2 nm).Moreover,it is found that the PLintensity and wavelength of denatured ovalbumin coated CdTe QDs are reversible duringheating (323 K)-cooling (278 K)cycles.All the studies provide an important theoreticalbasis for searching temperature-insensitive bioprobes.(4)A new method to detect the ovalbumin was set based on the PL change.Chemically reduced ovalbumin had been used to modify the surface of CdTe QDs,resulting in the enhancement of PL intensity and the blue shift of the PL peak wavelength.A new method for the determination of ovalbumin was established based on the PLchanges.Under the optimal conditions,experiment results showed that the PL intensityand PL peak wavelength were both in good linear with the ovalbumin concentration in therange of 0.125μM～4μM and the detection limit was 0.03μM.The results werecompared with the traditional UV absorption method,and showed relatively goodreliability.(5)Water-soluble core/shell structure with CdTe cores capped by CdS shell(CdTe/CdS)were synthesized in aqueous solution with captosuccinic acid as stabilizer.The absorption and fluorescence spectra confirmed that the synthesized QDs had goodoptical properties.It was observed that the QY of QDs was greatly increased after a heating-cooling cycle (from 22% to 41%).Then the QDs were used to prepare fluorescentprobe.The experiment results showed that the transferrin could conjugate to CdTe/CdSQDs effectively and the HepG2 cells were recognized successfully.This work is of greatsignificance for the preparation of high-powered QDs and their applications in life science.And it has an important reference value for the recognition of cancer cells.(6)High quality of CdTe QDs were synthesized in aqueous solution with glutathioneas the stabilizer.UV-visible spectra and fluorescence spectra confirmed the as-synthesizedQDs had good optical properties.The two-step glutaraldehyde (G)method and one-step Gmethod were compared by the capillary electrophoresis to label con A.Experimentalresults showed that two-step G method has better labeling result.更多还原