【作者】 王燚；

【导师】 黄承志；

【作者基本信息】 西南大学 ， 分析化学， 2014， 博士

【摘要】 金属纳米颗粒因其独特的性质已广泛应用于传感、催化、成像、生物医药、光电器件、信息存储等领域。在分析化学领域,金属纳米颗粒由于具有独特的局域表面等离子体共振(LSPR)性质可作为优良的光学探针应用于生化传感和光学成像。其LSPR性质及应用效能与元素组成、形貌、尺寸及组装方式等参数密切相关。目前,基于金属纳米颗粒的LSPR在光分析化学中的应用研究方面仍存在一些局限,例如：难于根据实际需求合成高质量的金属纳米颗粒探针,纳米探针及其组装体的生物相容性和在生物介质中的稳定性较差,具有特定结构的纳米颗粒及其组装体的形成机制尚不清楚,难于通过调控纳米颗粒的结构来有效调节金属纳米颗粒的LSPR性质,基于纳米颗粒LSPR性质的分析传感方法重现性差等。本文针对金属纳米颗粒在合成、组装、以及基于纳米颗粒LSPR性质的光分析化学应用中存在的问题开展了以下两方面的研究内容：1.金属纳米颗粒的合成与组装(1)使用生物相容的壳聚糖衍生物同时作为还原剂和稳定剂,发展了一种简单、“绿色”的方法实现了金纳米颗粒的一步法合成与组装。首先,通过对壳聚糖的侧链进行改性,得到一种新颖的壳聚糖-茚三酮复合物。然后,利用这种多聚糖衍生物与Au3+的结合以及氧化还原作用,在生理温度下制备了生物相容的类球形金纳米颗粒。这种多聚糖衍生物还能作为稳定剂吸附于所形成的金纳米颗粒表面。由于其在纳米颗粒表面不均匀分布,导致金纳米颗粒部分晶面相对裸露,从而使金纳米颗粒通过偶极-偶极相互作用发生自组装形成一维的链状结构。相比单分散的金纳米颗粒,这种各向异性的金纳米链表现出截然不同的LSPR性质,其消光光谱随组装程度的增大向长波长处发生明显的红移。(2)进一步验证了上述一步生长与组装制备金纳米链的方法普适性,探讨了各向异性的一维组装体的LSPR性质,并对纳米颗粒同时生长与组装的机制进行了系统和深入的研究。以另一种多聚糖(右旋糖酐)作为模板分子,在强氧化剂的作用下首先制备了一种含有丰富醛基的多聚糖衍生物,即多聚醛右旋糖酐。利用这种新的多聚糖衍生物同时作为还原剂和稳定剂,也实现了金纳米颗粒的一步法合成与组装。通过对反应条件如反应物浓度、反应时间、温度等参数的系统调节,可以有效地调控各向异性的金纳米链的组装程度,从而调节其LSPR性质。机理研究进一步证明了纳米颗粒间的偶极-偶极相互作用以及纳米颗粒表面稳定剂分子间的氢键作用是金纳米颗粒进行组装的主要驱动力。(3)除了一步合成与组装方法,我们还利用富含胸腺嘧啶的寡核苷酸序列与汞离子之间的特异性识别作用,通过两步法实现了金纳米棒以“头碰头”方式的组装,并探讨了纳米棒之间的距离、组装方式与近场等离子体共振耦合作用之间的关系。首先,利用巯基与金纳米颗粒表面的共价键合作用将富含胸腺嘧啶的寡核苷酸序列修饰到金纳米棒的端部；由于两个胸腺嘧啶碱基可以与一个汞离子进行特异性结合而形成T-Hg2+-T结构,诱导两个金纳米棒的端部相连,从而使金纳米棒以“头碰头”方式进行组装。通过设计不同长度的寡核苷酸序列,可以实现精确控制纳米棒之间的距离,从而操控纳米棒之间的等离子体共振耦合作用。这种基于受体-配体分子特异性识别作用来组装纳米颗粒的方法可以被拓展到其它纳米组装体和纳米器件的制备中。2.金属纳米颗粒在光分析化学中的应用(1)发展了一种简单的方法在室温下合成右旋糖酐包被的金纳米颗粒,并基于这种金纳米颗粒的LSPR性质进一步将其作为光学探针用于色度法检测降血压药硫酸双肼屈嗪。利用本方法合成的金纳米颗粒具有均一的粒径和优良的生物相容性,且在较高离子强度的介质中具有较好的稳定性。双肼屈嗪分子中的两个肼可与金纳米颗粒表面的醛基发生反应形成腙,从而通过桥联作用减小金纳米颗粒之间的距离甚至使其发生团聚。基于反应前后金纳米颗粒LSPR性质的变化,可以实现对尿样中硫酸双肼屈嗪的定量检测,标准加入回收率为98.3-102.5%。(2)金属纳米颗粒的LSPR散射性质使其可以作为优良的光学探针用于成像研究。我们利用非共价键作用将金属纳米颗粒锚定在氧化石墨烯的表面,制备了一种金属/碳纳米材料杂化组装体,并利用金属纳米颗粒的LSPR性质在普通暗场光学显微镜下“点亮”不具有光信号的石墨烯。本方法中,首先通过巯基和金属的共价键作用将具有特定序列的寡核苷酸序列修饰到金或银纳米颗粒的表面,再通过寡核苷酸碱基与石墨烯之间的π-π堆积作用将金属纳米颗粒锚定在石墨烯表面。由于金和银纳米颗粒具有较强的LSPR散射信号,石墨烯的轮廓和位置可以在光学显微镜下被清晰地观察到。这种集合了金属纳米颗粒和石墨烯特殊性质的复合材料有望在生物成像、药物传送及癌症治疗中发挥重要作用。(3)金属纳米颗粒的LSPR散射性质还能用于特定化学反应的原位和实时监测。在普通的光学显微镜下,我们实时地监测了单个银纳米立方体的氧化腐蚀过程。结合暗场光学成像系统和扫描电子显微镜,银纳米颗粒在氧化腐蚀过程中的不同阶段所表现出的光学信号和形态均可以被观察到,从而清楚地阐释了金属纳米颗粒的氧化腐蚀机理。理论模拟的结果也证实了氧化腐蚀优先从银纳米立方体的顶角处开始进行,这是由于顶角处与{100}晶面相比具有较高的界面自由能。本方法及相关技术手段可以使我们更深入地了解纳米颗粒在各种化学反应和生物过程中的行为。总之,本论文在发展简单高效的金属纳米颗粒的合成与组装方法基础上,探讨了影响金属纳米颗粒LSPR性质的关键因素,并将金属纳米颗粒作为光学探针成功应用于分析传感和光学成像。因此,本论文解决的关键科学问题是通过研究金属纳米颗粒LSPR性质与其物性参数之间的关系,构建了基于金属纳米颗粒光分析传感和成像的新方法。本论文将为金属纳米材料的合成与组装提供充分的实验依据和崭新的思路,并将拓展金属纳米颗粒的LSPR性质在光分析化学和光学成像中的应用。更多还原

【Abstract】 Metal nanoparticles have been widely used in sensing, catalysis, imaging, biomedicine, optical and electronic devices, and information storage due to their unique properties. Owing to the unique localized surface plasmon resonance (LSPR) properties, metal nanoparticles can act as excellent optical probes in analytical chemistry (e.g., optical sensing and imaging). The LSPR properties of metal nanoparticles as well as their performances in various areas are closely related to the element, morphology, size, assembly mode, and other parameters. However, the applications of metal nanoparticles in analytical chemistry on the basis of their LSPR are still challenging. For example, researchers are usually hard to obtain metal nanoparticles with high quality according to the requirements for applications; the biocompatibility of the nanoparticles and their stability in biological medium is usually bad; the mechanisms of the growth and assembly of metal nanoparticles with a specific structure are not very clear; it is difficult to tune the LSPR properties of the metal nanoparticles for the applications in analytical chemistry; the reproducibility of some nanoparticle-based analytical methods is not satisfied. To address these issues, we have systematically studied the synthesis and assembly of metal nanoparticles as well as their applications in photoanalytical chemistry. This thesis includes the following two parts:Part I Synthesis and assembly of metal nanoparticles, including the following three parts:A simple, one-pot, and "green" method was developed for the simultaneous synthesis and self-assembly of Au nanoparticles, using a biocompatible polysaccharide derivative, chitosan-ninhydrin (CHIT-NH) conjugate, as both a reducing agent and a stabilizer. Firstly, the side chain of chitosan was modified with ninhydrin through covalent bond, and a novel CHIT-NH conjugate could be obtained. Then, we achieved the synthesis and assembly of quasi-spherical Au nanoparticles at physiological temperature through the interaction between CHIT-NH conjugate and Au3+. This new macromolecule could also act as a stabilizer and thus adsorb on the surfaces of the formed Au nanoparticles. Due to its uneven distribution on the surfaces, some facets of the Au nanoparticles were exposed and thus induced the self-assembly of Au nanoparticles into nanochains via dipole-dipole interaction. Compared to the dispersed Au nanoparticles, the LSPR extinction spectrum of the anisotropic Au nanochains red shifts to a longer wavelength.Then, we further studied the universality of the above strategy for the simultaneous growth and self-assembly of Au nanoparticles, as well as systematically studied the LSPR properties of the anisotropic assemblies and explored the mechanism involved in such synthesis. Using another polysaccharide, dextran, as a template, we prepared a new polyaldehyde dextran (PAD) through a redox reaction between dextran and a strong oxidant. With PAD as both a reducing agent and a stabilizer, we also achieved the biomimetic synthesis and assembly of Au nanoparticles via a one-pot approach. The morphology of Au nanochains could be controlled through adjusting the reaction conditions such as the concentration of reagents, reaction time and temperature. Mechanism investigations further suggest that dipole-dipole interaction between nanoparticles and the intermolecular hydrogen bonding of stabilizers are the main driving forces for the assembly of Au nanoparticles.Except for the one-pot method, we also developed a two-step and versatile approach for the end-to-end assembly of Au nanorods by means of the specific molecular recognition between thymine (T)-rich oligonucleotides and mercury (Ⅱ). Moreover, the relationship between the near-field plasmon coupling of Au nanorods and their distances or assembly modes were also discussed. For the assembly of Au nanorods, the T-rich DNA was firstly conjugated to the ends of Au nanorods through thiol-Au covalent. Then, the T-T base pairs could strongly bind up and readily form a structure of T-Hg2+-T configuration in the presence of Hg2+ions, inducing the assembly of Au nanorods in an end-to-end mode. By designing the DNA sequence, we could precisely control the distance between the nanorods and thus manipulate their plasmon coupling. This strategy for the assembly of nano-scaled materials, which relies on the receptor-ligand molecular recognition, can be extended to the fabrication of other nanomaterial assemblies and devices.Part II The applications of metal nanoparticles in photoanalytical chemistry, including the following three parts: Firstly, we developed a simple approach to the preparation of dextran-capped Au nanoparticles at room temperature, and further used them as optical probes for the colorimetric detection of an antihypertensive drug (dihydralazine sulfate) on the basis of their unique LSPR properties. The as-obtained Au nanoparticles were uniform in size, biocompatible, and very stable even if in a medium of high ionic strength. The hydrazine groups of dihydralazine sulfate are able to react with the aldehydes on the surface of Au nanoparticles to form hydrazone, resulting in the decrease of the spacing of nanoparticles. Based on the change of LSPR properties of the Au nanoparticles, we could quantificationally determine dihydralazine sulfate in uric samples with the the recovery in the range of98.3-102.5%.Metal nanoparticles can also act as a signal reporter for optical imaging based on their unique LSPR light scattering. We proposed a noncovalent strategy to fabricate metal nanoparticle/graphene oxide (MNP/GO) hybrids and achieved the direct illumination of graphene in dark-field microscopic system. DNA-founctionalized Au/Ag nanoparticles could anchored on the surfaces of GO through π-π interaction between DNA bases and GO. Owing to the strong LSPR scattering of MNPs, the profiles of graphene could be clearly observed using an ordinary optical microscope. This graphene-involved composite which has collective properties can be promising candidates in a variety of applications such as bioimaging, drug delivery, and cancer therapy.Finally, we used the LSPR scattering properties of metal nanoparticles for real-time and in situ monitoring of the chemical reactions. With the aid of an ordinary optical microscope, we achieved the real-time observation of the oxidative etching of an individual Ag nanocube. The optical information and morphology of the Ag nanoparticles at different stages of the etching process could both be obtained, which clearly elucidated the mechanism of the oxidative etching on metal nanoparticles. In addition, the results from theoretical simulation also confirmed the mechanism that the oxidative etching of an Ag nanocube tends to start from its corners due to the relatively high energy at these sites relative to{100} facet. This strategy will enable us better understand the behaviors of nanoparticles in a variety of chemical reactions and biological processes.In conclusion, we have developed simple and efficient methods for the synthesis and assembly of metal nanoparticles. Meanwhile, the key parameters affecting the LSPR propertise of metal nanoparticles have also been systematically investigated. Then, the well-defined metal nanoparticles were used as probes for optical sensing and imaging. Therefore, the main contribution of the thesis is that it has developed new strategies for the optical sensing and imaging based on the LSPR properties of metal nanoparticles. This thesis will provide sufficient experimental evidences and new insights for the synthesis and assembly of metal nanomaterials. Moreover, it expands the applications of metal nanoparticles in analytical chemistry and optical imaging.更多还原