【作者】 谢超；

【导师】 任吉存；

【作者基本信息】 上海交通大学 ， 应用化学， 2010， 博士

【摘要】 免疫分析是利用抗原与抗体之间的高特异性反应实现对抗体、抗原或相关物质进行检测的分析方法。免疫分析是一种非常重要的生物分析方法,它被广泛地应用于临床诊断、食品和环境分析、生物及医学研究等领域。目前免疫分析主要以微孔板为实验平台的异相分析模式。这种方法需要抗体的包埋,缓慢的异相免疫反应,多次耗时的冲洗,酶放大反应和离线检测分析等步骤。因此,这种方法操作繁琐、分析时间长、不能满足某些快速检测和诊断的要求。均相免疫分析不需要分离,能够直接测定免疫反应混合体系中的待测物(抗体或者抗原)。这种方法通常快速,而且很容易实现微型化和自动化。目前某些检测方法如荧光偏振、荧光共振能量转移、生物发光能量转移被用于均相免疫分析。然而,由于这些检测方法的灵敏度较低,不能满足临床检测的要求。本论文旨在基于单分子和单颗粒技术,发展高灵敏的均相免疫新方法,用于肿瘤标志物的分析。主要研究工作包括如下几个方面:1)基于荧光自相关光谱和互相关光谱,发展了均相免疫分析方法。为了克服荧光相关光谱在研究分子间相互作用时,需要分子量相差4倍的限制,本文构思了两个策略,即采用荧光交叉相关光谱系统和减小抗原分子的分子量。首先,我们构建了一种新型的单激光激发的荧光交叉相关光谱系统。采用量子点这种新型的荧光纳米材料为探针,以人IgG和羊抗人IgG的免疫反应为研究模型,构建了均相免疫分析检测系统。基于该系统我们测定了免疫复合物的浓度及其特征扩散时间与动力学半径。实验结果表明单激光激发的荧光交叉相关光谱系统克服了现有的荧光交叉相关光谱的仪器结构复杂和操作繁琐的缺点,成功地消除了Cross-talk效应。然后,我们以人工合成的多肽为免疫抗原,基于荧光自相关光谱方法,建立了一种均相竞争免疫分析方法。由于多肽抗原具有和生物抗原一样的生理活性,而且容易制备,使它成为一种理想的抗原。其主要优点是分子量小,能满足荧光自相关光谱对分子量的要求。我们利用这个策略系统地研究了肿瘤标志物CA125抗原与其抗体的免疫反应,对该竞争免疫反应的灵敏度、特异性、可逆性、解离常数、解离速率等进行了研究。研究结果表明该方法灵敏度约为0.1 nM,可以用于某些较高含量的组分测定。2)基于金纳米粒子(Gold Nanoparticles,GNPs )在溶液中的布朗运动和共振散射效应,我们提出了一种高灵敏的单个金纳米粒子检测新方法,称之为单个金纳米粒子计数法(Single Gold Nanoparticles Counter,SGNPC)。它的工作原理是在高聚焦的激光束中,GNPs由于布朗运动和共振散射效应在检测的微区内(小于1 fL检测体积)产生强的光子爆发。实验表明光子爆发数与GNPs浓度之间存在非常好的线性关系(R=0.992)。本文系统地研究了某些因素对单个GNPs信号的影响,发现GNPs的光子爆发强度随其粒径和激发光强度增大而显著增强。我们考察了合并时间(Bin-time)和测定时间对检测灵敏度的影响。在优化的条件下,对36 nmGNPs的检测限为17 fM,线性范围为17 fM到170 pM。该方法具有很好的重现性,光子爆发数计数的日内和日间重现性(相对标准偏差,RSDs)分别为4.1% (n=11)和3.6 %(n=7)。进而,我们将SGNPC方法成功地与微流控芯片联用。研究了在一定流速下,GNPs光子爆发数与其浓度和流速的关系。实验结果表明在一定的压力场下,GNPs的光子爆发数与其浓度同样具有很好的线性关系。同时,在相同浓度下,GNPs溶液的流速越大则爆发数越多,其检出限越低。我们相信SGNPC方法以及SGNPC与微流控芯片联用系统在均相生物分析领域中具有重要的应用前景。3)基于SGNPC方法和GNPs标记技术,发展一种高灵敏的均相免疫分析新方法。在均相免疫分析中采用夹心免疫模式,分别将两种抗体修饰在GNPs探针上。当这两种抗体-GNPs探针加入含有目标物(抗原)的样品中,它们将与目标物的结合,会导致GNPs形成二聚物(或者低聚体)。随着目标物增加,溶液中的GNPs数目会随之减少。SGNPC可根据光子爆发数的改变来检测GNPs数目上的变化。基于这种单颗粒技术建立了肿瘤标志物如癌胚抗原(CEA)和α-胎蛋白(AFP)的均相免疫分析方法。在优化的条件下,CEA和AFP的检测限分别为130 fM和714 fM,该方法比现行的均相免疫分析方法的检测限低2个数量级。该方法成功地用于健康个体与癌症患者血清中CEA和AFP浓度的测定。测定的结果与ELISA分析结果基本一致。与现行的方法相比,我们方法具有灵敏度高、操作简便、分析时间短等特点。原理上我们的方法适用于各种临床免疫分析和药学上的生物分子识别反应的监测。更重要的是,该方法的检测体积少于1 fL,样品的用量可以缩减到nL水平,可能成为均相免疫分析中高通量检测平台。4) GNPs具有非常强的光吸收和散射性质,被成功地应用于生物标记、基因载体和光热治疗等领域。GNPs的粒径对其光学和化学性质有至关重要的影响。然而,在GNPs的生物应用中,我们缺乏一种有效的方法对溶液中GNPs(及其连接物)的粒径和粒径分布进行表征。因此我们提出了一种共振散射相关光谱技术(Resonance Light Scattering Correlation Spectroscopy,RLSCS)表征GNPs粒径分布的新方法。该方法基于共振散射相关光谱技术,将遗传算法(GA)用于散射相关函数曲线解析,从而获得GNPs的粒径和粒径分布。我们首先参照荧光相关光谱的理论,提出了散射相关光谱技术表征GNPs粒径分布模型,然后用计算机进行模拟。在模拟中,首先预设了各种粒径分布模式,通过计算求得其对应的相关曲线,用Matlab程序实现了遗传算法。结果表明遗传算法-共振散射相关光谱(GA-RLSCS)获得的结果与预设的初值基本吻合,从理论上说明了GA-RLSCS能够用于对GNPs的粒径和尺度分布的表征。进而,将该方法用于溶液中GNPs的粒径及其粒径分布的表征。GA-RLSCS方法得到的结果与TEM的结果基本吻合。GA-RLSCS方法测量快速(30 s)、样品需求量少(μL级),将在生物分析如免疫分析、核酸杂交、Aptamer识别等方面有广泛的应用前景。更多还原

【Abstract】 Immunoassay is based on highly selective immune reaction of antigen with antibody, and can be used to determine antigen or antibody. Currently, immunoassay becomes one of very widely used analytical technologies in clinical diagnosis, food and environmental analyses and biological and biomedical studies. The conventional heterogeneous immunoassays mainly use a microwell plate as an assay platform, and this method is considered to be labour intensive and time-consuming due to the use of tedious separation and washing steps before signal measurement. Compared to heterogeneous assays, homogeneous assay is to directly determine analytes in immune reaction mixture. This method is usually fast and amenable to miniaturization and automation. To date, several analytical methods have been used in homogeneous immunoassays, which mainly include fluorescence polarization, fluorescence resonance energy transfer, bioluminescence resonance energy transfer, surface plasmon resonance, and chemiluminescence. However, most of the homogeneous immunoassays do not have enough sensitivity, and they have currently been not satisfied for certain requirements in clinical diagnosis.In this dissertation, on the basis of single molecule/nanoparticle detection techniques, we develop highly sensitive homogeneous immunoassays for cancer biomarkers and biological macromolecules. The main contributions are as follows:1) We develop homogeneous immunoassay methods based on fluorescence correlation spectroscopy (FCS) and fluorescence cross correlation spectroscopy (FCCS). To distinguish the two components in FCS analysis, their diffusion coefficients must differ by a factor of at least 1.6, which corresponds to a molecular weight ratio of 4. In order to overcome the limitation, we use two strategies that are using fluorescence cross-correlation spectroscopy (FCCS) model and decreasing the antigen molecular weight. Firstly, we established a FCCS setup with single wavelength laser. Using quantum dots as labeling probes, the homebuilt setup was successfully applied for the study of the homogeneous immunoassay reaction. We used the immune reaction of human immunoglobulin G with goat antihuman immunoglobulin G as a reaction model. The molecule numbers in a highly focused volume, the concentration, and the diffusion time and hydrodynamic radii of the reaction products can be determined by FCCS system. The results demonstrated that the single wavelength FCCS system has simple instrument structure and operation process. The cross-talk effect was almost completely suppressed. This FCCS system was adapted to homogeneous immunoassay. Secondly, we develop a homogeneous competitive immunoassay method based on FCS using synthetic peptides as a tracer antigen. Synthetic peptides were peptide-mimic of the native antigen, and usually are short protein sequences, which can be recognized by corresponding antibodies. Synthetic peptides represent ideal antigenic targets for immunoassays since they can be cheaply and easily produced in large scale and in a reproducible manner. The most important thing is that synthetic peptides antigens have low molecule weight, which satisfied the requirement of FCS for molecule weight. We systematically investigated the immune reaction of CA125 (cancer biomarker) peptide antigen and its antibody, and obtained the dissociation constants and dissociation rates. Furthermore, we evaluated the sensitivity, specificity, reversibility, dissociation constant and dissociation rate of this competitive immunoassay. Our data illustrated that the detection limit of homogeneous immunoassay method based on FCS was about 0.1 nM. This method possesses potential applications.2) We present for first time an ultrasensitive method for detection of small gold nanoparticles, call as single gold nanoparticle counter (SGNPC). Its principle is based on the photon burst counting in a highly focused laser beam due to Brownian motion and strong resonance Rayleigh scattering of GNPs. We systematically investigated the effects of certain factors on the photon burst intensity. The photon burst intensity markedly depended on the laser wavelengths and power and GNPs sizes. The results demonstrated that the relationship between the photon burst counts and GNPs concentration showed an excellent linearity (R=0.992). The linear range was over four orders of magnitude, and the detection limit was 17 fM for GNPs (36 nm).The reproducibility of the photon burst counting was quite satisfactory and the relative standard deviations (RSDs) for intra-day and inter-day were 4.1 % (n=11) and 3.6 % (n=7), respectively. Moreover, our method was successfully applied for single gold nanoparticle detection in micro-fluidic chip channel. The results showed that there was the excellent linearity relationship between the photon burst counts and GNPs concentration under a given pressure. In addition, lower detection limit was obtained by increasing the velocity of GNPs flow. We believe the combination of SGNPC with a micro-fluidic chip have great potential applications in homogeneous bioassays.3) On the basis of SGNPC technique, we developed an ultrasensitive detection platform for homogeneous immunoassays for cancer biomarkers. A sandwich format is used in homogeneous immunoassays. We conjugated two antibodies to GNPs based on the strong adsorption of GNPs to antibodies. When GNPs-antibody conjugates are mixed in a sample containing antigens, the binding of antigens will cause GNPs to form dimmers (or oligomers). The number of GNPs decreased with an increase of antigens in solution, and SGNPC sensitively detected the change in the number of GNPs according to the photon burst counts. We used this technology to construct homogeneous immunoassays for AFP and CEA. The detection limits were 130 fM for CEA, 714 fM for AFP. Our method was successfully applied for direct determination of CEA and AFP levels in sera from healthy subjects and cancer patients. The results were in good agreement with ELISA assays Compared to current methods, our method can be characterized as extremely high sensitivity, good selectivity, simplicity and short analysis time. Furthermore, SGNPC can be used for real-time monitoring of certain biochemical processes in vitro and vivo due to its high spatial and good time resolutions. More importantly, our detection volume is less than 1 fL, and the sample requirement can be reduced to nano liter level. Therefore, our method has the potential to become a high-throughput detection platform for homogeneous immunoassay.4) Gold Nanoparticles (GNPs) possasse very strong absorption and scattering properties and currently, are extensively used in several fields of biological labeling, gene carrier and photothermal therapy sensing. The mean size and the size distribution of GNPs play a paramount important role in these applications. So far, we lack effective methods for characterization of GNPs in aqueous solution. Herein, we presented a novel method to determine the size and size distribution of GNPs in solution at single particle level, called as resonance light scattering correlation spectroscopy (RLSCS). We presented a data-fitting algorithm for RLSCS based on Genetic Algorithms to invert particle-size distribution from RLSCS curves. According to FCS method, we established a theoretical model of GNPs size distribution GNPs using RLSCS technique. We performed computer simulations to verify the validity of the method by using different size distributions modes. In this study, we firstly suppose certain size distributions modes, and then got the correlation curves by calculation, and finally Genetic Algorithms (GA) was used to invert the size distribution from autocorrelation curve of GNPs. GA program was written in Matlab language. The results showed that GA-RLSCS could retrieve initial values exactly. This result demonstrated that theoretically, GA-RLSCS could be used to measure size and size distribution. Variable sizes of GNPs were measured by this method. The results agree reasonably with that obtained by TEM. Compared with current methods, our method is simple, reliable, and may become a useful tool for characterization of GNPs and other nanoparticles. We believe that RLSCS may become an effective method for immunoassay, nucleic acid hybridize and aptamer recognition.更多还原