【作者】 吴世嘉；

【导师】 王洪新； 王周平；

【作者基本信息】 江南大学 ， 食品科学， 2013， 博士

【摘要】 稀土元素掺杂的上转换荧光纳米颗粒具有长波长激发（通常是近红外光或者红外光），短波长（紫外光或者可见光）发射的特殊光学性质，可以有效的避免生物样本自发荧光对检测的干扰，对于提高检测灵敏度和准确性具有重要意义。微生物毒素污染是引发食品安全问题的重要因素，对微生物毒素的检测也是食品安全分析中的重要指标。本论文研究了稀土元素掺杂的上转换荧光纳米颗粒作为新型荧光纳米标记物在微生物毒素检测中的应用。建立了一系列灵敏、快速、可靠以及多组分同时检测的新方法，为保障食品安全提供了有利手段。首先，通过水/溶剂热法合成了稀土元素掺杂的上转换荧光纳米颗粒，研究反应条件，得到发光性能好，形貌均匀，纳米级的上转换荧光颗粒。随后，利用硅烷化或者配体交换的方法对上转换颗粒的表面进行改性，使得材料在水相中分散性好，并且带有生物官能团，为进一步生物功能化修饰提供了条件。通过透射电镜，荧光光谱，X射线衍射，傅里叶变换红外光谱，紫外光谱等表征结果证明上转换荧光纳米颗粒的制备和修饰成功。其次，研究上转换荧光纳米颗粒在激光诱导荧光方法中的应用。将表面经过修饰的上转换纳米颗粒连接核酸片段，磁性纳米颗粒连接核酸适配体，通过核酸杂交使得上转换纳米颗粒与磁性纳米颗粒连接，加入被测物质后由于适配体与靶物质的特异性结合导致部分上转换颗粒与磁性颗粒解离，在外界磁场分离富集的作用下得到上转换和磁性颗粒的复合物，980nm红外激光激发下得到上转换荧光发射。通过该实验设计观察目标物赭曲霉毒素A浓度与荧光信号的关系，实现了上转换荧光纳米颗粒标记-适配体识别-磁富集的激光诱导荧光检测赭曲霉毒素A的新方法，检出限为0.0001ng·mL-1。第三，在上转换荧光纳米颗粒成功应用于单组分的激光诱导荧光检测的基础上研究了双色上转换荧光纳米颗粒标记技术。选择荧光光谱互相不重叠的两种上转换荧光纳米颗粒分别标记两种目标物质，在980nm红外激光激发下得到两组荧光发射峰，实现同时对两组目标物质进行定量检测。一方面，将两种上转换荧光纳米颗粒标记毒素人工抗体，在竞争免疫反应的模式下，成功建立了同时检测黄曲霉毒素B1和赭曲霉毒素A的新方法，检出限均为0.01ng·mL-1；另一方面，将两种上转换荧光纳米颗粒标记核酸序列，与目标核酸序列杂交识别，成功建立了同时检测两种手足口病病毒EV-71和CV-A16的新方法，检出限分别为20pmol/L和25pmol/L。本实验也为多色上转换荧光标记技术在定量分析检测中的发展打下了基础。第四，研究上转换荧光纳米颗粒作为荧光能量供体在荧光共振能量转移中的应用。分别将上转换荧光纳米颗粒和金纳米颗粒（作为荧光能量受体）标记在分子信标两端组成荧光共振能量转移体系，此模式下结合适配体识别和磁分离富集效应检测伏马菌毒素B1，检出限为0.01ng·mL-1。随后进一步深入探索了将双色上转换纳米颗粒同时作为荧光能量供体的模式，发现利用氧化石墨烯作为荧光能量受体，能够同时淬灭多种不同发射的上转换荧光，根据这种现象我们首次提出了多重荧光共振能量转移理论，即同一种荧光能量受体同时淬灭多种荧光能量供体。基于以上设计原理将伏马菌毒素B1和赭曲霉毒素A的适配体分别与两种上转换荧光纳米颗粒连接同时作为荧光能量供体，使其吸附到氧化石墨烯表面从而荧光淬灭，实现了多重荧光共振能量转移模式下同时对伏马菌毒素B1和赭曲霉毒素A的检测，检出限分别达到0.1ng·mL-1和0.02ng·mL-1。该研究工作扩大了荧光共振能量转移的应用，寻找发射光谱可被区分的荧光材料作为荧光能量供体，多重荧光共振能量转移模式可以应用于更多组分目标物质同时检测。第五，研究上转换荧光纳米颗粒配合激光诱导荧光检测技术中放大检测信号提高检测灵敏度的方法。除了利用磁性纳米颗粒分离富集外，还结合了一种酶催化目标物循环信号放大的方法。针对以适配体结合靶物质的识别模式，选择核酸外切酶I能够特异性的高效的酶切单链核酸适配体，从而导致本来与适配体结合的目标物质重新释放再与新的适配体结合，目标物质在检测体系中被循环利用，引起了信号的放大，提高了检测灵敏度。实验中以上转换荧光为信号检测了金黄色葡萄球菌肠毒素B，发现在核酸外切酶I的作用下灵敏度提高50倍，检出限为0.3pg·mL-1。激光诱导上转换荧光方法由于上转换荧光本身的特点其检测灵敏度非常高，结合酶催化信号放大可以进一步提高灵敏度，解决超痕量毒素难以被检测的问题。总之，本论文制备了稀土元素掺杂的上转换荧光纳米颗粒这一新型的荧光材料作为荧光标记物，利用其特殊的光学性质，配合以激光诱导荧光、荧光共振能量转移、适配体识别、免疫识别、分子杂交、磁分离富集、酶催化放大等等技术手段，构建了一系列新颖的、灵敏的、特异性的、稳定的、实用的分析方法用于食品中微生物毒素单一组分或多组分的同时检测，为保障食品安全提供了有力的技术支持。更多还原

【Abstract】 Due to the unique property of rare earth doped UCNPs that emitted shorter wavelength(ultraviolet or visible light) under excitation by longer wavelength (usually near-infrared lightor infrared light) via a two-photon or multi-photon mechanism, the autofluorescence ofbiosamples could be effectively avoided. It had a profound significance on improving thesensitivity and accuracy of detection methods. Microbial toxins contamination are the primaryunsafety factors which causing food security problem, and the related detections were veryimportant to food safety analysis. In this dissertation, rare-earth-doped upconversionnanoparticles (UCNPs) were applied in microbial toxins analysis detection. The applicationsof UCNPs as a kind of novel fluorescent nano-labels were researched in quantitative analysisof microbial toxins in foods. Based on advantages of UCNPs, a series of sensitive, rapid,reliable and simultaneous analytical methods were developed, and those methods couldprovide a guarantee for food safety.Firstly, based on the solvothermal technology and optimization condition, therare-earth-doped nanoscale UCNPs which had good fluorescent property and uniformmorphology were synthesized. And the silanization groups or ligand exchange were thensuccessfully modified on the surface of UCNPs. Furthermore, the modified UCNPs wereapplicable for bio-functionalization due to their biological functional groups andwell-dispersed in aqueous solution. The synthesis and modified of UCNPs were characterizedby transmission electron microscope (TEM) image, fluorescence spectrum, X-ray diffraction(XRD), fourier transform infrared (FT-IR) and ultraviolet spectrophotometer (UV).Secondly, the applications of UCNPs in the field of laser induced fluorescence (LIF)detection were researched in this section. In brief, aptamers were immobilized onavidin-conjugated magnetic nanoparticles (MNPs), and their complementary DNA werelinked to avidin-conjugated UCNPs, then the aptamers hybridized with the complementaryDNA to form the duplex structure, therefore were assembled on to the surface of MNPsgiving a background fluorescent signal. In the presence of analyte, the aptamer preferentiallybond with analyte and caused the dissociation of some complementary DNA, liberating someUCNPs-labeled complementary DNA. Then the remaining of UCNPs-MNPs compoundswere separated with an external magnet, and excited by980nm infrared laser. Based onUCNPs labeling, aptamer affinity and magnetic separation, a novel analytical method hasbeen successfully applied to the detection of ochratoxin A (OTA) related to the intensity ofUCNPs and the detection limit was0.0001ng·mL-1.Thirdly, the applications of dual-colour UCNPs labeling were researched in this sectionbased on the UCNPs successfully used in single LIF detection. Two sets of emission peakswhich could be easily distinguished in spectrum by980nm laser, belonged to differentUCNPs were chosen as dual-colour labels for determination two kinds of analytes. In onedesign pattern, two kinds of UCNPs were used to conjunct with antibodies of aflatoxin B1(AFB1) and ochratoxin A (OTA) respectively. A novel competitive fluorescent immunoassayfor the simultaneous detection of AFB1and OTA using UCNPs as dual-colour labels was developed. The detection limit of AFB1and OTA were0.01ng·mL-1. In another designpattern, two kinds of UCNPs were firstly used to conjunct with the signal nucleic acids, andthen hybridized with target nucleic acids. A novel sandwich type fluorescence analysis forsensitive and selective detection of enterovirus71(EV-71) and coxsackievirus A16(CV-A16)by dual-colour UCNPs labeling technology was also successfully established, and thedetection limit was20pmol/L and25pmol/L, respectively. The results suggested thatdual-colour UCNPs labeling-based fluorescent assay was applicable and promising for thesensitive detection. This assay could also be extended to the detection for various analytesbased on multicolour labeling of UCNPs.Fourthly, the applications of UCNPs as fluorescent energy donors in fluorescenceresonance energy transfer (FRET) were researched in this section. In one design pattern, wepresented a new aptasensor for fumonisin B1(FB1) based on FRET between UCNPs and goldnanoparticles (AuNPs). The quenchers (AuNPs) were attached to the5’ end of the molecularbeacon (MB), and the donors (UCNPs) were attached to the3’end of the MB. The good resultof detection was benefited from UCNPs labeling, aptamer affinity and magnetic concentration.The detection limit was0.01ng·mL-1. Furthermore, the new FRET system based ondual-colour UCNPs as fluorescent energy donors was explored. Graphene oxide (GO) werefound as the entire and effective acceptor because of a good overlap between the fluorescenceemission of dual-colour UCNPs and the absorption spectrum of GO. Hence, a multiplexedFRET system has been first presented and applied on the basis of multiplexed energy donorsto the entire energy acceptor. We have constructed a novel sensor for the simultaneousdetermination of ochratoxin A(OTA) and fumonisin B1(FB1) using a multiplexed FRET fromaptamers modified dual-colour UCNPs on the surface of graphene oxide, and the detectionlimit was0.1ng·mL-1and0.02ng·mL-1, respectively. Our study has paved the way to widenthe applications of FRET systems: the multiplexed FRET-based detection can be used forvarious targets with fluorescence nanoparticles of which emission spectra can bedistinguished as donors.Fifthly, the signal amplification of UCNPs by laser induced fluorescence method wasresearched in this section. Enzyme-catalysed target recycling strategy was an effectiveamplification approach except for magnetic separation and concentration. Against to thecomplex of aptamer and target, exonuclease I, an exonuclease specific to single-strandedDNA, was used to amplify the signal of UCNPs and improve the sensitivity of detection byselectively digesting a particular DNA for analyte recycling. An ultrasensitive bioassay wasdeveloped to detect staphylococcal enterotoxin B (SEB) using UCNPs labeling and anexcellent limit of detection of0.3pg·mL-1was obtained by exonuclease-catalysed targetrecycling strategy. The sensitivity of LIF method was high because of the advanced propertyof UCNPs, and even higher sensitivity was displayed because of exonuclease-catalysed targetrecycling strategy. It was a significant method to solve the problem of ultratrace toxins hard todetect in foodstuffs.In conclusion, lanthanide doped upconversion nanoparticles were synthesized asfluorescent labels in this study. Based on its unique luminescent properties, a series of novel,sensitive, specific, stable and practical assays were developed for the determination of microbial toxins in food coupled with laser induced fluorescence, FRET, aptamer recognition,immnuo-recognition, DNA hybridization, MNPs separation and concentration, andexonuclease-catalysed target recycling strategys. Moreover, multicolor UCNPs fluorescentlabels were successfully applied in food safety analysis and detection, which provide atechnical support for guaranteeing food safety.更多还原