【作者】 刘剑波；

【导师】 王柯敏；

【作者基本信息】 湖南大学 ， 分析化学， 2011， 博士

【摘要】 量子点(QDs)由于其独特的尺寸依赖的光物理性质,作为一种优异的荧光纳米材料,受到研究者的广泛青睐。随着量子点制备工艺、表面修饰技术的不断完善以及功能应用研究的不断拓展,基于量子点的纳米表征技术在化学生物分析等领域显示出越来越广阔的应用前景。本论文瞄准这一重要的研究方向,在对当前迅速发展的量子点进行大量文献调研的基础上,以量子点纳米颗粒作为出发点,以荧光技术作为主要分析手段,结合材料制备技术、光学成像技术、纳米分析技术等,将量子点的制备、分析检测应用以及高灵敏光学成像作为研究主线,主要开展了以下几个方面的工作:一、发展了以油胺-硒化氢复合物为前体的脂溶性量子点制备方法。首先利用硒的还原作用和硫酸的酸化反应,并结合油胺对于硒化氢的吸收富集作用,制备了油胺-硒化氢复合物。然后,以这种复合物作为前体,采用溶剂热合成步骤,制备了脂溶性CdSe量子点。所制备的量子点为立方晶型,荧光光谱跨越较宽,从480 nm到610 nm连续可调;荧光半峰宽较窄,均在25 nm至40 nm之间;最高量子产率达到23%,光稳定性较强。在此基础之上,还进行了量子点的壳层包被,制备了CdSe/ZnS量子点。本部分工作发展了一种无须使用三烷基膦,相对价廉和环保的脂溶性量子点制备方法,为进一步的表面修饰、功能组装以及分析检测应用奠定了基础。二、基于氟硼酸根离子对水溶性CdTe量子点的化学刻蚀作用,发展了一种简单、温和的量子点尺寸调控方法。在NaBF4溶液中,随着时间的延长,水溶性CdTe量子点尺寸逐渐减小,吸收光谱和荧光发射波长发生连续蓝移。量子点被刻蚀的原因可能是由于氟硼酸根离子对Cd(II)的解离以及表面氧化作用。这种量子点的刻蚀在中性水溶液中进行,条件温和,便于控制,可以得到一系列不同荧光发射波长的量子点。该方法为量子点的尺寸、光谱调控提供了一种新的手段,可以进一步应用于其它含镉化合物的刻蚀研究以及纳米器件的加工制作等领域。三、结合物理包埋和共价交联的方法,发展了一种量子点琼脂糖凝胶微球(AHM)的包被技术。首先,巯基乙胺修饰的量子点利用表面氨基与琼脂糖羟基的氢键相互作用,基于物理作用扩散进入琼脂糖微球中,得到量子点琼脂糖微球复合物(QDAHM),平均每个微球包被的量子点数目高达6.0×107。然后引入聚乙烯亚胺(PEI)和乙二醛,与量子点表面氨基反应形成共价网络结构,得到PEI包被的QDAHM(QDAHM/PEI)。采用该方法得到的QDAHM/PEI不仅具有较高的颗粒包被量和共价稳定性,并且pH稳定性得到提高,成功构建了量子点荧光编码微球复合物。该量子点复合物有望应用于多目标筛选以及阵列检测等领域。四、基于氟离子对量子点的分散效应,发展了一种降低量子点团聚和非特异性吸附作用的简单方法。氟离子加入巯基乙胺表面修饰的CdTe量子点溶液中,显著提高了量子点的胶体稳定性,降低了颗粒之间的团聚,这主要因为氟离子与氨基形成氢键,屏蔽了颗粒之间的氢键相互作用。并且发现,低浓度氟离子的存在,可以降低量子点对于玻片和细胞的非特异性吸附作用,并显著提高量子点的表面交联效率。该工作提供了一种简单便利的提高量子点稳定性的离子介导法,为量子点的分析检测和细胞成像提供了保障。五、基于量子点的可逆团聚机制,发展了一种氟离子的纳米荧光开关探针。巯基乙胺-CdTe量子点基于颗粒之间的NHN氢键作用发生团聚,荧光自淬灭;氟离子加入,形成更强的NHF氢键,诱导量子点的分散,荧光得到恢复。基于荧光的恢复作用构建了量子点的荧光开关探针,应用于水相体系氟离子的检测,检测下限可达到5.0μM,且特异性好、响应速度快。本工作不仅提供了一种简单便利的水相溶液中氟离子的检测方法,也为量子点荧光探针的设计提供了新的构建模式。六、基于自行搭建的单颗粒荧光成像平台,开展了不同功能化磷脂修饰的量子点性能差异的研究。首先采用磷脂二硬脂酰磷脂酰乙醇胺(DSPE)和聚乙二醇-二硬脂酰磷脂酰乙醇胺(PEG2000-DSPE)分别修饰脂溶性CdSe/ZnS量子点,将其转换为水溶性。然后采用单颗粒成像技术,比如荧光涨落光谱、单颗粒荧光强度分析、单颗粒示踪分析等,对于两种磷脂化的量子点进行了实时、动态的光物理性质的研究。对比分析结果表明DSPE-QDs分散性较差,单颗粒荧光较强,扩散系数较小,体现为多个量子点包被形式;PEG2000-DSPE-QDs则单分散性较好,扩散系数较大,体现为单个量子点包被形式。二者性能差异主要因为是磷脂分子末端聚乙二醇分子修饰的差异造成的。本工作不仅提供了一种纳米颗粒的实时、动态的单颗粒成像研究方法,并且发展了不同结构性能的磷脂化量子点。七、基于量子点单颗粒荧光成像和荧光共定位方法,实现了蛋白质的高灵敏检测。以凝血酶为模型,基于其两个核酸适体的识别作用构建了三明治检测体系,利用全内反射荧光显微镜,在单分子水平上基于荧光共定位方法实现了凝血酶的高灵敏检测,检测下限为0.8 pM。该方法充分利用了量子点“一元激发、多元发射”的发光特性,避免了样品分离纯化等过程,为蛋白质的高灵敏分析检测提供了新的思路。更多还原

【Abstract】 Semiconductor quantum dots (QDs), as novel fluorescent nanomaterials, have attracted much interest due to their unique size-dependent optical properties. With the development of their synthetic techniques, surface processability and functional applications, QDs play important roles in the fields of chemical and biological analysis. Aiming at this important research field, based on a survey of a large number of documents, combining with materials preparation, optical imaging and nanometer analysis, by taking fluorescence technique as the main analytical approach, the preparation, their analytical detection and imaging of QDs as the line of this dissertation, following several works have been performed.1. Oleylammonium-selenide complex was exploited as a new precursor for synthesis of hydrophobic QDs. H2Se gas was firstly generated by reduction and subsequent acidation of Se powder. The gas was then introduced into oleylamine, which led to the formation of oleylammonium-selenide complex. The complex was used as precursor for preparation of hydrophobic CdSe QDs via hot-injection solvothermal synthetic procedures. The characterization results showed that the proposed method led to the formation of hexagonal wurtzite CdSe QDs with narrow fluorescence full-width at half-maximum (25 ~ 40 nm), high photoluminescence quantum yield (up to 23%), and a broad emission spectra tunable from 480 ~ 610 nm. Furthermore, core/shell CdSe/ZnS QDs were prepared. This work provides a low cost and environmentally benign technique for QDs preparation due to the absence of trialkylphosphine, and the obtained QDs with excellent properties could be further used in the fields of surface modification, nanomaterials assembly and analytical detections.2. A facile and mild chemical etching method was developed for resizing of CdTe QDs. Treated with BF4-, CdTe QDs gradually decreased in size and this was accompanied by corresponding blue-shifts of both the absorption and fluorescence spectra. The chemical etching process may involve both the removal of Cd dangling bonds by BF4- and the assistance of surface oxidation. The etching was performed at room temperature under neutral conditions, and different sizes of CdTe QDs could be obtained through termination of the etching reaction at different time intervals. This novel etching technology provides a means of downsizing and tailoring of the QDs and has great potential for the architecture of multifunctional nanostructures3. A strategy of combining physical embedding and covalent crosslinking was developed to encapsulate cysteamine-capped QDs into agarose hydrogel microbeads (AHM). Cysteamine-capped QDs were encapsulated into the pores of agarose hydrogel microbeads by virtue of hydrogen bonding between the amino groups of cysteamine and hydroxyl groups of agarose, resulting in more than 6.0×107 QDs per microbead. Polyethylenimine (PEI) and oxalaldehyde were then introduced to form a covalent cross-linked network to further stabilize the encapsulation. The resulting hybrid hydrogel microbeads exhibited high doping capacity and negligible QDs leaching. Furthermore, the microbeads possessed elevated fluorescence stability at wide pH ranges and two-color barcoded hydrogels were successfully obtained. We envision that further optimization of this method will allow high-through screen and array analysis of the hybrid hydrogel microbeads technology.4. A simple ions-mediated dispersing technique was developed to reduce the aggregation and non-specific adsorption of QDs. By the introduction of F- ions, the self-aggregation of cysteamine-capped QDs was disassembled, and the stability of QDs was greatly enhanced. We inferred the disaggregation was from the substitution of NHF hydrogen bonds for NHN hydrogen bonds of cysteamine-capped QDs. Meanwhile, we found in the presence of F- ions, the non-specific adsorption of QDs on the glass slides and cell was greatly decreased. Furthermore, the chemical cross-linking efficiency of QDs with biomolecules was greatly improved in the presence of F- ions. This work not only provides a new strategy for reducing the aggregation and non-specific adsorption of QDs, but also provides a guarantee for the following biomedical imaging and chemical sensing.5. A switchable fluorescent QD probe for F- ions was developed based on the aggregation/disaggregation mechanism. The cysteamine capped CdTe QDs undergo spontaneous self-aggregation via NHN hydrogen bonds, which results in efficient fluorescence self-quenching. In the presence of F- ions, the aggregates disassemble due to the substitution of NHF hydrogen bonds for NHN hydrogen bonds, which results in fluorescence recovery of the QDs. Thus, the fluorescence off/on process enables us to quantitate F- ions in aqueous media. This design provides a novel means for nanoscopic sensing, which has the advantage of rapid, simple, sensitive, and specific detection, with a limit of detection of 5.0μM for F- ions. This work provides a new signal transduction mechanism for QDs-based sensors and the methodology developed here may be expanded for design of other fluorescence nanoparticle sensors.6. A single nanoparticle imaging technique was set up to study the structure and photophysical properties of different phospholipid encapsulated QDs. Firstly, hydrophobic CdSe/ZnS QDs were phase transferred into water soluble by phospholipids derivatives, 1,2-distearoyl- sn-glycero-3- phosphor- ethanolamine (DSPE) and 1,2-distearoyl-sn- glycero-3- phosphoethanolamine- N-[methoxy(polyethylene glycol)-2000] (PEG2000- DSPE), respectively. Fluorescence fluctuation spectroscopy, fluorescence intensity statistic analysis, and single particle tracking were then executed to study the two types of phospholipid encapsulated QDs. The results showed that compared to DSPE-QDs micelles, PEG2000-DSPE-QDs micelles possessed higher monodispersity, narrower size- distribution, lower fluorescence intensity and lower diffusion coefficients. Hence, we inferred that statistically, many QDs were embedded in one DSPE-QDs micelle, while one QD was embedded in one PEG2000-DSPE-QDs micelle. The single nanoparticle imaging techniques can be further used for real time, in situ, dynamic biomedical research. In addition, the phospholipid encapsulation approach allows different ligands functionalized on the surface of QDs, to satisfy the particular requirements of the analytical applications.7. Fluorescence colocalization method was emplyed for sensitive protein detection. By taking the advantage of the robust fluorescence of QDs and high flexible total internal reflection fluorescence microscopy technique, fluorescence colocalization imaging of QDs at single nanoparticle level can be achieved. Thrombin employed as a protein model, we demonstrate a sandwich structure for protein detection using multicolor aptamer-functionalized QDs as nanoprobes. The presence of target protein can be determined based on colocalization measurements of the nanoassemblies. A low of detection with 0.8 pM was obtained. The fluorescence colocalization method broke the optical diffraction limit and reached nanometer resolution. Meanwhile, the method utilized the multicolor QDs, avoiding the separation and purifying process. Hence, this work provides a simple, fast procedure for sensitive protein detection at single nanoparticle level.更多还原