Study On Optical Biosensing Based On Functionalized Nanoparticles

Based on the quantum dots and gold nanoparticles which have excellent optical property and good biocompatibility, this paper discusses the preparation of functional nanomaterials combining with the strong affinity and identification ability to nucleic acids and antigens/antibodies. Many new nano-optical biosensing systems are constructed on the basis of quantum dots and gold nanoparticles. The detection of target molecules can be achieved by the nano-optical biosensing systems which are simple, sensitive, rapid and specific.This paper consists of five chapters. The first chapter is the introduction which briefly introduces the research background of nanomaterials and presents an overview on the optical property and synthesis of quantum dots and gold nanoparticles. It focuses on the detection principle, characteristics and applications of the two sorts of functionalized nanoparticles in the biological markers and biosensing field, and reveals the research background, purpose, and significance of this paper.The second chapter is homogeneous fluorescence-based immunoassay via inner filter effect of gold nanoparticles on fluorescence of CdTe quantum dots. Homogeneous immunoassays are becoming more and more attractive for modern medical diagnosis because they are superior to heterogeneous immunoassays in sample and reagent consumption, analysis time, portability and disposability. Herein, an universal platform for homogeneous immunoassay, using human immunoglobulin (IgG) as a model analyte, has been developed. This assay relies upon the inner filter effect (IFE) of gold nanoparticles (AuNPs) on CdTe QDs fluorescence. The immunoreaction of antigen and antibody can induce the aggregation of antibody-functionalized AuNPs, and after aggregation the IFE of AuNPs on CdTe QDs fluorescence is greatly enhanced, resulting in a decrease of fluorescence intensity in the system. Based on this phenomenon, a wide dynamic range of1～100pg/mL for determination of IgG can be obtained. The proposed method shows a detection limit of0.3pg/mL for human IgG, which is much lower than the corresponding absorbance-based approach and compares favorably with other reported fluorescent methods. This immunoassay method is simple, rapid, cheap, and sensitive. The proposed method has been successfully applied to measuring IgG in serum samples, and the obtained results agreed well with those of the enzyme-linked immunosorbent assay (ELISA).The third chapter reveals fluorescence analysis of DNA by exonuclease Ⅲ-assisted amplification method in the presence of gold nanoparticles. The research designs DNA functionalized gold nanopaticles probes, which complement and hybridize with DNA probe of labeled fluorescein (FAM) and the target DNA. Since fluorescence resonance energy transfer (FRET), the fluorescence of FAM is quenched by gold nanoparticles. In the presence of exonuclease Ⅲ (Exo Ⅲ), due to Exo Ⅲ catalytic and removal effect to specificity of double-stranded DNA, DNA probe labeled with FAM is gradually catalyzed and removed. FAM and the target DNA are released. The fluorescence is recovered, since the separation of gold nanoparticles and FAM. And then, the released target DNA would be turned to next step for the catalytic and removal process with the effect of Exo Ⅲ. Thus, the fluorescence signal is amplified after multiple cycles, so as to establish a new method for the determination of the target DNA; moreover, to expand the application of functionalized gold nanoparticles in optical biosensor field.The fourth chapter discusses the simultaneous determination of thrombin and ATP with homogeneous fluorescence analysis method of dual-color quantum dots. The research prepares functionalized quantum dots with fluorescence analysis method, combined with many merits of the quantum dot including tunable and wide the absorption spectrum, narrow and symmetric emission spectrum, high fluorescence efficiency, strong anti-light bleaching and controllable size, etc., thus synthesizes different size quantumn by controlling the reaction conditions, which were covalently incorporated at one end of the aptamer. The quantum dot fluorescence is quenched under the super quenching effect of single walled carbon nanotubes (SWCNTs). After adding the respective ligand, the effect of quantum dots and SWCNTs are weakened due to the combined effect of aptamers-ligand specific recognition. The quantum dot fluorescence is restored. The different quantum dots are excited at the same excitation wavelength. The simultaneous determination of the respective fluorescence intensity of quantum dots are finished; thereby the quantity of different ligand concentration can be analyzed, and the simultaneous determination analysis method to multiple homogeneous fluorescence of different analytes are established as well.The fifth chapter introduces the determination of carcinoembryonic antigen on the basis of analysis to chemiluminescence immunoassay of luminol-silver nitrate catalyzed by gold nanoparticles. As one of the most common tumor markers, Carcinoembryonic antigen is widely used as indicators of a variety of tumors in the diagnosis and monitoring of the digestive system. Therefore, the monitoring to carcinoembryonic antigen has very important clinical significance. With the rapid development of nanomaterials, nano-materials as a catalyst in the chemiluminescent reaction aroused extensive attention. Since many merits of gold nanoparticles including easy preparation, high catalytic activity, good biological compatibility, etc., and combined with merits of chemiluminescence analysis method such as high sensitivity, simple instrument, low background signal, wide linear range and rapid analysis, the research puts forward chemiluminescence immunoassay method with antibody-labeled functionalized gold nanoparticles catalyzed luminol-silver nitrate system for the determination of carcinoembryonic antigen, improves the sensitivity and stability of the method, pushes detection limit as low as0.2pg/mL, and overcomes the shortcomings of traditional immunoassay method such as the time-consuming, labor-intensive, high cost, and so on.