The Research On Piezoelectric Immunosensors Based On Mixed Self-Assembled And Hyperbranched Polymers

Recently, the piezoelectric immunosensors have been applied in the biological and environment analytes areas with simple-operation, high-sensitivity, low-cost and non-pollution etc. But the research point still is how to make them to be applied in clinical detection by improving the immobilization and lowing the non-specific absorption. In this paper, new immobilized methods and immunosensors were developed based on the lab previous research. The detail contents are as follows:(1) Mixed self-assembled monolayer (SAM) modified on the surface of Au nanoparticles can resist nonspecific adsorption and enhance the immobilization amount of the antigens. The thiols forming mixed self-assembled monolayer are long-chain and the strategy includes layer-by-layer scheme. But the long-chain thiols maybe curve round Au nanoparticles and therefore decrease the immobilization amount of the antigens and produce nonspecific adsorption. In the meantime, it requires multiple preparation steps during which possible corruption of the film may occur via the repetitive immersion and rinsing process. In this paper (Chaper 2), the short-chain thiols (Cysteamine and 6-mercapto-1-haxanol) were self-assembled onto Au nanoparticles to form the mixed SAM-capped Au nanoparticles which were further covalently bound on the 3-Mercaptopropionic acid (MPA)-modified gold electrode. Based on the strategy, a novel piezoelectric immunosensor for the detection of thyroid hormone T4 was developed.(2) A new quartz crystal microbalance (QCM) immunosensor based on self-assembling gold nanoparticles to the electropolymerized polytyramine (Pty) film was developed for the detection of thyroxine (T4) (in Chaper 3). A Pty film was firstly electropolymerized on the surface of the QCM; subsequently a self-assembled nano-gold layer was applied on the Pty film in order to immobilized anti-T4 antibodies; finally through the immunoreaction of anti-T4 antibodies with T4, the detection of T4 was realized. A series of experimental conditions were investigated including immunoreaction time, concentration of anti-T4 antibody etc. Comparing to the glutaraldehyde binding and Cysteamine methods, the self-assembling gold nanoparticles showed larger frequency response and less non-specific adsorption.(3) A new QCM immunosensor based on cysteamine self-assembled monolayer and Hyperbranched polymer (HB)/chitosan adsorption procedure has been developed for the detection of hIgG (in Chaper 4). Cysteamine self-assembled monolayer firstly was applied to the surface of the QCM, and a strong negatively-charged HB monolayer, which had been actived with 1-Ethyl-3-(3-dimethylamino-propyl) carbodiimide hydrochloricde (EDC), and N-hydroxysuccinimide (NHS) previously, was attached on the cysteamine by the strong force between -NH2 and -COOH. The positively-charged chitosan was then electrostatically posed on the crystal in order to immobilized Au-(goat anti-hIgG antibodies). Finally through the immunoreaction of goat anti-hIgG antibodies with hIgG, the detection of hIgG was realized. A series of experimental conditions were optimized in detail. The immunosensor fabricated with proposed method can offer large frequency response, good selectivity etc.(4) In this paper, a QCM immunosensor based on a novel biosensing interfacial by the absorption of self-assembled HB/Chitosan mixed-SAM monolayer and protein A has been developed for the determination of IgG (in Chaper 5). With the activation of EDC/NHS, the positively-charged chitosan and negatively-charged HB were linked each other by the strong force between -NH2 and -COOH and formed the mixture of HB and chitosan. HB/Chitosan mixed-SAM monolayer was first applied to the gold electrode surface by dipping the crystal into the mixture, protein A was then electrostatically adsorbed on the crystal in order to orientation-immobilize antibodies. A series of conditions of immobilizing antibodies were discussed in detail. Analytical results indicate that the immunosensor with this immobilization procedure can provide large frequency shift and better selectivity.