【作者】 穆亲；

【导师】 钟新华； 李艳；

【作者基本信息】 华东理工大学 ， 无机化学， 2014， 博士

【摘要】 由于量子限域效应,纳米材料内在的物理或化学性质随粒子尺寸的改变而改变。半导体纳米晶(又称量子点)的量子限域效应最直观的表现就是材料的能带宽随粒子尺寸的变小而增大。因此可以通过合成不同大小的纳米晶来调节其能带宽度,从而实现用同一种纳米晶材料得到不同波长的发射荧光。相对于传统的有机染料,荧光量子点具有更好的光稳定性且呈现连续的吸收光谱。上述性质使得量子点相比于有机染料更适合于长时间的观测并具有更宽广的激发波长范围,从而使得单一光源可同时激发多种不同发光颜色的量子点进而实现多通道观测。此外,量子点还具有窄且对称的发射光谱,高的发光强度(单个粒子的发光强度约100倍强于单个有机染料分子)及比普通有机染料更长的荧光寿命。上述优越的荧光性质使得荧光量子点成为一种潜在的取代传统有机染料的理想荧光基团,并在分析检测和生物医学示踪成像等领域中受到研究者们越来越多的关注。基于量子点出色的光学性质,本论文以量子点作为发光材料来构建量子点荧光探针,并成功实现了对Hg2+、多巴胺以及生物硫醇的痕量快速检测。主要的研究内容如下：(1)利用量子点构筑比例荧光探针并用于Hg2+的检测毒性重金属离子的检测始终是环境监测领域中的一个重要课题。本论文中,我们设计并制备了一种可视化检测水溶液中Hg2+的量子点比例荧光探针。首先根据量子点荧光光谱随尺寸可调的性质,我们制备出分别发红光和绿光的CdTe/CdS量子点,然后将红色荧光的量子点包裹在二氧化硅纳米粒子内部,再把绿色荧光的量子点连接在氨基化的二氧化硅纳米粒子表面从而构筑出双波长发射的比例荧光探针。Hg2+与绿色荧光的量子点之间发生电子转移,导致绿光量子点荧光强度随Hg2+浓度的增大而逐渐猝灭；但包裹在二氧化硅内部的红色荧光量子点却由于有硅层的保护而不会受到Hg2+的影响,其荧光强度也基本不受环境中Hg2+的影响,因而基本保持不变。因此可根据两种量子点荧光强度比值的变化而引起的溶液发光颜色改变来实现对Hg2+的快速可视化检测。在紫外灯照射下,随着Hg2+浓度的增大,探针溶液从黄绿色逐渐变为红色。在我们的实验条件下,探针对Hg2+的检测限可以达到3.1nM。实验结果表明,该探针对Hg2+显示出较好的识别能力,常见金属离子基本不会对Hg2+的检测产生影响。此外,将该探针用于测定生物样品中Hg2+浓度也可以得到较为满意的结果。(2)腺苷包覆的量子点荧光探针检测多巴胺多巴胺是一种与神经传导有关的生物小分子,人体中多巴胺的缺失可能会导致一些神经性的疾病。多巴胺在水溶液中很容易发生氧化,生成多巴胺醌,而多巴胺醌则是一种良好的电子受体。基于多巴胺的这一性质,我们构筑了一种可有效检测多巴胺的量子点荧光探针。首先通过配体交换的方法,采用商用廉价的腺苷作为水溶性配体,从高质量的油溶性CdSe/CdS/ZnS量子点制得了腺苷配体包覆的水溶性量子点,然后利用腺苷与多巴胺醌之间的非共价相互作用将多巴胺醌吸附到量子点表面,在激发态的量子点与多巴胺醌之间发生电子转移,导致量子点的荧光猝灭,从而成功实现对多巴胺的高灵敏性检测。该探针对多巴胺具有优异的选择性,其它常见氨基酸的存在不会影响探针对多巴胺的检测,且该探针还可以将多巴胺与采用电化学方法检测时易对其产生干扰的抗坏血酸和尿酸区分。在我们的实验条件下,探针对多巴胺的检测限可以达到29.3nM。另外,该探针也可成功应用于对生物样品中多巴胺的检测。(3)利用水相合成的CdTe/CdS量子点检测生物硫醇生物硫醇(如谷胱甘肽、半胱氨酸、高半胱氨酸)参与了人体内许多重要的生命活动,人体中生物硫醇的异常变动会引起许多严重的疾病。因此,实现对生物硫醇的快速实时检测对于疾病的诊断及治疗都具有十分重要的意义。本论文中,我们直接采用水相合成的巯基丙酸包覆的CdTe/CdS量子点,利用量子点与TiO2纳米粒子之间的电子转移导致量子点荧光猝灭以及生物硫醇与量子点表面金属离子的强配位作用阻碍量子点与TiO2纳米粒子之间的电子转移从而使量子点荧光得以恢复的机理,设计了一种可以检测水环境中生物硫醇的量子点荧光探针。具体检测原理如下：当TiO2纳米粒子加入到量子点溶液中时,量子点表面的巯基丙酸配体与TiO2纳米粒子表面的Ti原子之间的形成的共价键,使得量子点被吸附到TiO2表面。由于TiO2的导带能位低于量子点的导带能位,故光生电子能够从量子点的激发态注入到TiO2纳米粒子的激发态,从而导致量子点的荧光猝灭。当生物硫醇加入到TiO2与量子点的混合体系中时,生物硫醇因具有比巯基丙酸更强的配位能力,取代了原来量子点表面的巯基丙酸配体,增大了TiO2纳米粒子与量子点之间的距离,从而阻碍了量子点与TiO2纳米粒子之间的电子转移,使量子点的荧光得以恢复,进而达到检测生物硫醇的目的。三种生物硫醇对量子点荧光恢复能力的大小依次为谷胱甘肽>高半胱氨酸>半胱氨酸。在最优化的实验条件下,CdTe/CdS量子点探针对谷胱甘肽、半胱氨酸和高半胱氨酸的检测限分别为0.17μM,0.28μM和0.15μM。探针对生物硫醇显示出良好的选择性和抗干扰能力,其它19种天然氨基酸的存在不会对生物硫醇的检测结果造成干扰。此外,将该探针用于对生物样品中谷胱甘肽的测定也得到令人满意的结果。另外,通过将量子点固定在普通的滤纸上,我们还成功地制得了一种可以快速方便的检测水溶液中谷胱甘肽的指示试纸,从而为生物硫醇的快速便捷检测提供了一个平台。更多还原

【Abstract】 Due to quantum confinement effect, the inherent physical or chemical properties of nanoscaled materials could be tuned by changing their particle sizes. One of the intuitionistic performances of quantum confinement effect in semiconductor nanocrystal (also called quantum dots, QDs) is that the energy band gap of QDs increases upon the reduction of particle size. Therefore, different emission wavelengths can be achieved with use of the same kind of nanomaterial with different particle sizes. Compared to traditional organic dyes, QDs exhibit better photostability and continuous absorbance spectra. These properties make QDs more suitable in long-time investigation and bring forward a wider range of excitation wavelengths for QDs. Thus QDs with different emission colors can be excited by a single excitation wavelength, allowing multiplexed detection. Furthermore, QDs have narrow and symmetrical emission spectra, high emission intensity (the emission intensity of an individual particle is about100times stronger than a single dye molecular) and long fluorescence lifetime. These advantages make QDs alternative emitter for super-sensitive, multicolored, and long-time detection, tracing and imaging in biomedicine. In recent years, QDs have attracted more and more interests in the area of analysis and biological imaging. In this dissertation, QDs are used as the luminescence materials to build fluorescence probes for the selective and sensitive detection of Hg2+, dopamine and biothiols. The main research contents are as follows:(1) QDs-based ratiometric fluorescence probe for the detection of Hg2+The analysis of toxic heavy metal ions is always an important issue in environment monitoring. Ratiometric fluorescence probes that can significantly eliminate the external effects by self-calibration of two different emission bands are preferable for the detection of real samples. Here, we designed a dual-emission QDs nanocomposite as a ratiometric probe to visually detect Hg2+in aqueous solutions. The dual-emission QDs nanocomposite consists of two differently sized CdTe/CdS QDs. The red-emitting larger sized CdTe/CdS QDs were embedded in silica nanoparticles, while the green-emitting smaller sized ones were covalently conjugated onto the silica nanoparticles surface. The addition of Hg2+can only quench green fluorescence in the dual-emission QDs nanocomposites because of the electron transfer between green-emitting QDs and Hg2+. However, the red-emitting QDs were insensitive to Hg2+due to the protection of SiO2shell, and their fluorescence intensities were accordingly barely changed. The quenching of green fluorescence triggered the change of fluorescence intensity ratio of two different emission wavelengths and hence induced the evolution of fluorescence color of the probe solution with the variation of Hg2+concentration. Based on this feature, the dual-emission QDs nanocomposites can be used to develop a ratiometric fluorescence probe for visual detection of Hg2+. Under UV-light irridation, with the increasing of the Hg2+concentration, the emission color of the probe solution changed from yellow-green to red gradually, which could be directly observed by naked eye for visual detection of Hg2+. In our experimental conditions, the detection limit can reach up to3.1nM. The probe also displayed good selectivity to Hg2+under the existence of other common metal ions. In addition, it had been successfully used in the determination of Hg2+in biological samples.(2) Adenosine capped QDs based fluorescence probe for the detection of dopamine.Dopamine (DA) is a kind of neurotransmitter, its deficiency in human body may lead to some neurological diseases. DA is very susceptible to be oxidized in aqueous solution, generating dopamine quinone (DAQ), which is a good electron acceptor. According to this property of DA, a QDs based fluorescent probe was synthesized for highly sensitive and selective detection of DA. In this assay, adenosine served as a capping ligand or stabilizer for QDs to render initial oil-soluble QDs with high quality dispersed in water; and as a receptor for DA to attach DA onto the surface of adenosine capped QDs. DA molecules can bind to adenosine capped QDs via non-covalent bonding, resulting in the fluorescence quenching of QDs due to the electron transfer between QDs and DAQ, thus enabling the detection of DA. The A-QDs based fluorescence probe showed a limit of detection of ca.29.3nM for DA detection. This facile method exhibited high selectivity and anti-interference in the presence of amino acid, ascorbic acid (AA), uric acid (UA) and glucide with100-fold higher concentration. Moreover, it was successfully used in the detection of DA in the human urine samples with quantitative recoveries.(3) CdTe/CdS QDs based fluorescence probe for the detection of biothiolsBiothiols (glutathione (GSH), cysteine (Cys), homocysteine (Hcy)) involved in a great number of important vital activities in human body, and unnormal alternations in the level of cellular thiols will cause many serious diseases. Thus, achieving rapid and instant detection of biothiols shows great significance for the diagnosis and treatment of illness. In this dissertation, we directly used water phase synthesized mercaptopropionic acid (MPA) capped CdTe/CdS QDs to design a fluorescent probe for the detection of biothiols in water environment. The quenched fluorescence of QDs attached to TiO2nanoparticles (TiO2NPs) was selectively switched on by biothiols through ligand replacement, which makes it feasible for facilely sensing biothiols based on the fluorescence turn on mechanism. The detailed principle is as follows:when TiO2NPs were added into the QDs solution, QDs were absorbed on the surface of TiO2NPs through the covalent bond between the terminal carboxyl group of MPA ligands and the Ti atoms on the surface of TiO2NPs, leading to the fluorescence quenching of QDs due to the electron injection from QDs to TiO2NPs. When biothiols were introduced into the QD-TiO2system, the MPA ligands on the surface of QDs may be replaced by biothiols due to the stronger coordination capacity of biothiols with metal ions on the QDs surface, and the distance between QDs and TiO2NPs is consequently enlarged. As a result, the initially quenched fluorescence of QDs is effectively recovered by the interruption of the electron transfer pathway. Based on the above features, a facil probe with excellent selectivity and high sensitivity was construced for simply sensing biothiols including GSH, Cys and Hcy. Under the optimal conditions, the detection limits of GSH, Cys and Hcy are0.17μM,0.28μM and0.15μM, respectively. The probe exhibited excellent selectivity and anti-interference ability, the presence of other19kinds of essential amino acids will not interfere with the detection of biothiols. The determination of GSH in biological samples also received satisfactory results. In addition, a novel fluorescent indicating paper was constructed by immobilizing the probe on a piece of filter paper to visually detect GSH in which only a UV lamp was used. The indicating paper provided a simple platform for facial and visual detection of biothiols.更多还原