【作者】 申钦鹏；

【导师】 姚守拙； 聂舟；

【作者基本信息】 湖南大学 ， 分析化学， 2013， 博士

【摘要】 Cu’催化的炔化物和叠氮化物的偶极环加成反应是“点击化学”的典型例子,该反应具有反应条件温和、产率高、副产物少等优点,已经大量用于生物大分子的标记。此外,这种点击化学反应对Cu’离子催化有很高的特异性,已经用于开发铜离子的生物传感方法。但传统的有机点击反应,需要较高的反应物浓度以及长时间的反应,并且检测限相对偏高。DNA模板有机合成(DTS)是一种极具创新性的技术。它能显著地增加反应分子的有效摩尔浓度。同时,通过DNA杂交,拉近了修饰在DNA上的小分子反应基团之间的距离,该方法能明显的加快反应速率。通过DNA将DNA相关技术引入到非天然合成反应中,有助于反应基团的识别、合成步骤的设计、反应选择性的提高以及反应的放大。基于上述优点,DTS在许多方面都有着广泛的应用前景,它是小分子库构建、生物活性分子筛选和多肽均相合成等的有效方法。然而,DTS在生物分析领域的应用仍处于起始阶段。虽然前人在这方面研究甚少,但DTS的内在优势和强大功能奠定了其在生物传感中应用的基础。基于以上考虑,并综合相关文献报道,本论文将点击反应与DTS反应相结合,利用DNA模板点击化学反应,开发了一系列新型的化学生物传感方法。此外,考虑到点击化学在生物大分子标记上的卓越贡献,本论文将点击化学引入到生物大分子自由基的检测上来,希望能开发一些更为简便的检测生物大分子自由基的方法。(1)构建了一种基于DNA模板点击化学反应的新型Cu2’的荧光检测平台。本方法利用DNA模板点击化学反应的高特异性用于目标分子识别,DNA链取代和磁珠分离作为信号的传导,高灵敏性的SYBR Green I染料作为信号输出。与传统的点击反应方法相比较,该方法具有更高的灵敏度和更低的检测限(290nM)等优点。此外,只需要把DNA上的叠氮基-炔基换成其他能形成共价键的功能基团就可以把该传感系统用于其他物质的检测。这为各种生物传感器的构建提供了一个很有潜在应用价值的通用平台。(2)由于在前一个工作中,需要磁珠分离过程,操作比较繁琐,而且检测时不是在均相里完成。因此,我们开发了一个更加简便的Cu2’传感方法,可以实现加入混合就能输出信号。这种方法是基于DNA模板点击反应生成的G四面体(G4)结构并用于高灵敏检测Cu2’的新型荧光传感方法。由于结晶紫与G4结合后能极大地增强其荧光强度,因而被选做信号输出分子。鉴于结晶紫能探测G4结构的变化,我们把一段富G序列的DNA分开成两段长度不等的短链DNA,然后通过DTS反应使其连接起来并形成分子内G4结构,而结晶紫可以用于识别这一结构的变化。由于DTS反应的高产率和点击化学的高特异性,这种传感器也展示了较高的灵敏度和选择性。此外,由于活细胞内含有丰富的谷胱甘肽(GSH),本方法可能用于生物体内的GSH/Cu(I)加合物检测。因此,以本方法为例,我们证明了通过合理设计后,DTS调控的分子内G4结构的形成在生物传感器的开发上具有良好的应用前景。(3)简便、可视化检测、可以实现现场化检测是未来分析检测方法的发展趋势,而比色分析则刚好符合这些要求。因此,我们提出了一种基于Cu’催化的点击化学反应和未修饰AuNPs作为比色指示剂的Cu2+比色检测的简便方法。用于点击反应的DNA探针由两部分组成：一部分是一条修饰了叠氮基团的单链DNA(ssDNA)与一条长链的ssDNA的部分碱基形成的双链DNA(dsDNA);另一部分是一条与长链中未杂交的碱基互补的炔基化标记的短链ssDNA。由于短链ssDNA与长链ssDNA形成的dsDNA的熔解温度很低,在没有Cu2’的情况下,这两个部分在溶液中是分开的。当溶液中存在Cu2’时,铜离子催化的叠氮-炔基的点击连接反应引起了DNA结构从分离的单链形式变为完整的双链DNA结构。由于ssDNA保护的AuNPs和dsDNA保护的AuNPs在盐溶液中的稳定性不同,因此可以通过调控未修饰的AuNPs的团聚,使其从红色变成蓝色,来监测这种DNA结构的变化。在最佳条件下,这种传感器具有较高的灵敏度,其线性范围是0.5-10μM,检测限可达到250nM。这种方法不需要对DNA进行“双标记”和对金纳米粒子进行表面修饰,从而大大减少了费用和简化了传感器的组装及分析过程。由于铜离子催化的炔基-叠氮基的点击化学反应的高特异性,本传感器能够在高浓度的其他环境相关金属离子共存下具有良好的选择性,符合实际样品的检测要求。(4)鉴于点击化学在生物标记上的成功经验,我们将点击化学引入到生物大分子自由基的捕获上来。提出了点击-捕获(Click-Trap)设计新概念,合成了多种环状硝酮类自由基捕获探针,并用质谱、核磁等进行了表征。将这些捕获探针对氧中心和碳中心的小分子自由基进行了ESR捕获实验。此外,具有点击功能的炔基标记的新型捕获探针(Click-DMPO)也用于蛋白质活性氧自由基的氧化性损伤的原位捕获实验。较之于免疫自旋捕获技术,本方法操作更为简单,勿需复杂的免疫实验操作；由于点击反应的优异性能,有利于对Click-DMPO和蛋白质形成的复合物进行进一步的修饰和检测。另一方面,DNA由于精确的碱基互补配对性质,在纳米自组装方面具有高度可控、可编码、可图案化、易于实现目标分子标记等天然优势。其自组装形成的DNA结构不仅可以在纳米尺度上实现复杂结构的精确组装,而且还具有良好的生物相容性,不仅是一种新型的生物纳米材料,而且在分析化学中有着潜在的应用前景。因此,研究基于DNA纳米结构的生物传感技术亦是一项重要和具有挑战性的工作。(5)发展了一种基于DNA纳米管的质量放大效应的荧光各向异性的高灵敏检测ATP的传感方法。一条长链的ssDNA探针包含了目标分子的核酸适配体序列的一部分以及用于自组装形成质量放大荧光各向异性值(FA)的DNA纳米管的碱基序列。另一条修饰荧光基团的ssDNA探针是另一部分ATP的核酸适配体序列。当ATP与这两条DNA探针结合在一起时,极大地增加了荧光ssDNA探针和ATP分子形成的复合物的分子质量,从而增加了溶液的FA值。该传感器展现了较高的灵敏度(检测限为0.5μM)和极强的选择性。结果表明,DNA纳米结构质量放大策略可以用于设计快速、灵敏、高选择性核酸适配体探针,实现对复杂生物样品中小分子的检测。更多还原

【Abstract】 Copper(I)-catalyzed alkyne-zide Huisgen cycloaddition, the best example of "Click Chemistry", was used as a powerful linking reaction in biomacromolecule functionalization because of its high yielding capability under mild conditions with little by-product. In addition, this click reaction was intended for the development of copper ion sensors owing to its great specificity to the catalysis of copper(I). However, these methods were based on conventional organic reaction resulting in long reaction time and relatively high detection limit.DNA-templated organic synthesis (DTS) is an innovative technology capable of significantly increasing effective molarity of reactants and reaction specificity as well as remarkably accelerating reaction rate through DNA-encoded smallmolecule and hybridization-mediated proximity. The introduction of DNA into organic reaction allows non-natural synthetic events to be recognized, programmed, selected and amplified by DNA-based technology. Because of these features, DTS has become a promising and potent method in the construction of small molecular library, bioactive molecule screening, and homogenous peptide synthesis. However, the application of DTS in the bio-analytical field is still in its infant stage. Although there are a few pioneer works, the intrinsic advantages and powerful function of DTS warrant further efforts to develop its biosensing applications.Based on the above considerations and relevant reports in the literature previously, we intigrated the click reaction with the DTS reaction, and thus developed a series of new chemo/biosensors by taking advantage of DNA-templated click chemistry. In addition, this click cycloaddition was intended for the detection of biomacromolecules free raddicals owing to its powerful linking ability.(1) A novel fluorescent strategy has been developed for sensitive turn-on detection of Cu2+based on the high efficiency of DNA-templated organic synthesis, great specificity of alkyne-azide click reaction to the catalysis of copper ions, the sequential strand displacement for signal transduction and high sensitive SYBR Green I dye as the signal output. In comparison with the previously reported Cu2+assays using conventional organic click reaction, this DTS-based strategy has multifaceted advantages including higher sensitivity and lower detection limit (290nM). Moreover, this strategy can be readily expanded to other sensing applications by facilely changing the DNA-functionalized reactants capable for covalent bond formation. Therefore, taking this method as an example, we demonstrate that the rational design of DTS reaction is a promising platform for developing biosensors.(2) In order to improve the shortcomings of above-mentioned method, such as the heterogenous detection as well as the requirement of labeling biotin and megnatic separation, a novel fluorescent biosensing strategy has been developed for sensitive turn-on detection of copper ions based on the DNA-templated click chemistry induced generation of intramolecular G-quadruplex structure. Compared with the above DTS-based biosensors requiring separation, this approach provides a straightforward and homogenous fluorogenic strategy to achieve "mix-and-read" detection. Crystal violet (CV) is chosen as a signal reporter because its fluorescence can be enhanced greatly via binding to G-quadruplexe. Inspired by CV’s fluorogenic property susceptible to G-quadruplex structure switch, we exploited CV to identify the integration of split-G quadruplex by DTS-caused chemical DNA ligation. This sensor shows high sensitivity and excellent selectivity because of the high yielding capability of DTS and great specificity of click chemistry. Since glutathione is abundant in living cells, this method has potential for detection of biological CuT. Therefore, this method as a representative demonstrates the great promise and potency of DTS-mediated G-quadruplex formation in biosensors development.(3) Simple and on-site application are the future development trends of analysis and detection methods, and the colorimetric assay appears to fulfill the necessary criteria. Herein, we developed a novel colorimetric copper(Ⅱ) biosensor based on the high specificity of alkyne-azide click reaction and unmodified gold nanoparticles (AuNPs) as the signal reporter. The clickable DNA probe consists of two parts:an azide group-modified double-stranded DNA (dsDNA) hybrid with an elongated tail and a short alkyne-modified single-stranded DNA (ssDNA). Because of low melting temperature of the short ssDNA, these two parts are separated in the absence of Cu. Copper ion-induced azide-alkyne click ligation caused a structural change of probe from the separated form to entire dsDNA form.This structural change of probe can be monitored by the unmodified AuNPs via mediating their aggregation with a red-to-blue colorimetric read-out because of the differential ability of ssDNA and dsDNA to protect AuNPs against salt-induced aggregation. Under the optimum conditions, this biosensor can sensitively and specifically detect Cu2+with a low detection limit of250nM and a linear range of0.5-10μM. The method is simple and economic without dual-labeling DNA and AuNPs modification. It is also highly selective for Cu2+in the presence of high concentrations of other environmentally relevant metalions because of the great specificity of the copper-caused alkyne-azide click reaction, which potentially meets the requirement of the detection in real samples.(4) The click reaction was introduced to the detection of biomacromolecules free raddicals owing to its powerful linking ability in biomacromolecule functionalization. We proposed a new concept of "Click-Trap". In this study, several kinds of cyclic-nitrone spin traps have been synthesized and characterized by ESI/MS,’H-NMR,13C-NMR and so on. These novel free radical trapping agents have been used to study small molecule free radicals including oxygen and carbon centered radicals. In addition, the alkyne functional spin trap (Click-DMPO) has also been used in situ to capture protein oxidative damged by reactive oxygen species (ROS). In contrast to immuno-spin trapping technology, the present method is simple and does not require complicated operations. Owing to the excellent performance of the click reaction, it is very convenient to further modify and detect the spin adduct of Click-DMPO and protein.On the other hand, DNA is a potent material for self assembly because of its precise base pairing, highly controllable and addressable assembly, ease for pattern fabrication and the labeling of functional cargos. DNA nanostructures formed by self-assembly are highly ordered and possessDNA nanostructures formed by self-assembly, have good biocompatibility. As a new type of bio-nano-materials, DNA nanostructures have shown wide application prospects in analytical chemistry. Therefore, the development of robust biosensors based on DNA nanostructures is also significant and challenging work.(5) We developed a DNA-nanotube-basd mass amplifying probe for sensitive fluorescense anisotropy detection of ATP. A long ssDNA probe consists of a half of targeting aptamer domain against ATP and molecular mass amplifying domain for the self-assembly of DNA nanotube. The other ssDNA probe, bearing a fluorescent molecule, is the other half of ATP aptamer sequences. When ATP binds to the probe, the molecular mass and FA value of the probe/target complex will significantly increase. This method shows high sensitivity (the detection limit is0.5μM) and excellent selectivity. The results indicate that DNA nanostructure mass amplifying strategy can be used to design aptamer probes for rapid, sensitive, and selective detection of small molecules by means of FA in complex biological samples.更多还原