Study On DNA Electrochemistry Biosensor Based On Dendrimer Composite Materials

With improved understanding of structure and function of human gene,and the development of the Human Genome Project,DNA diagnostics has become an important area of molecular biology and biotechnology studies. Nowadays, wide-scale genetic testing requires the development easy-to-use, fast, inexpensive, miniaturized devices. Many new biological technologies have emerged and found their applications in this field. Among them,DNA biosensors are rapidly developed and have received considerable attentions. Electrochemical biosensing of DNA hybridization is a novel and developing technique that combining biochemical, electrochemical , medical and electronic techniques. It is qualified for meeting the size,cost and power requirements of genetic testing. The high sensitivity of such devices, coupled to their compatibility with modern microfabrication technologies,portability, low cost (disposability), minimal power requirements, and independence of sample turbidity or optical pathway, make them excellent candidates for DNA diagnostics. Therefore, it is expected to have broad prospect of application in clinic examination of inherited diseases and drug screening.Depending on its designed structure, small scale, mono-dispersing function groups, dendrimers molecules have become the highest materials to research in the nanomaterial field. Since dendimers molecules first came up in the middle of 1980s, a great amount of dendimers with different function groups have been invented in the 20 years. There are several kinds of dendimers such as pure carbon hydrogen chain, other atom mixed, metal containing. In recent years, the focus has turned from synthesis of dendimers to its application, especially in the pharmaceutical. Newcomer and co-workers demonstrate that dendimers with positive charge can absorb the bio-substance with negative charge such as DNA. They prove the potential ability of dendimers to be the carrier of bio-active substance. At present, PAMAM is considered to be the best carrier which is used frequently.However, the method and material used to immobilize biomolecule is one of the crucial factors for improving the stability, selectivity and sensitivity of biosensor in the preparation, and the selection of appropriate indicator is also the key technology. Four new-style DNA electrochemical biosensors were prepared, and the interaction to the Avian Influenza gene sequences was studied in this paper. The dissertation is divided into four main parts:(1) A composite film has been prepared by electropolymerization of 2,6-Pyridinedicarboxylic acid (PDC) on the platinum electrode and combined with G5 poly(amidoamine) dendrimer (PAMAM). Then, a new DNA electrochemical biosensor was developed by immobilizing probe ssDNA on the composite film electrode. The immobilization and hybridization of probe ssDNA was studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry using [Fe(CN)6]3-/4- as the redox indicator. The experimental results showed that the electron transfer resistance (Ret) of the electrode surface increased after the immobilization of probe ssDNA on the composite film and rose further after the hybridization of the probe ssDNA with its complementary sequence.(2) The silver nanoparticles-silk fibroin film (AgNPs-SF) and amino-terminated G5.0 PAMAMhad been immobilised via layer-by-layer self-assembly methods on the bare Pt electrode. Then the ssDNA probe was anchored onto the composite film and the new-style DNA biosensor was fabricated in the end. The experimental results showed that the DNA biosensor can detect the Avian Influenza gene sequences simply and fastly by EIS.(3) The gold nanoparticles-silk fibroin film (AuNPs-SF) and amino-terminated G5.0 PAMAM had been immobilised via layer-by-layer self-assembly method on the bare Pt electrode. Then the ssDNA probe was anchored onto the composite film and the new-style DNA biosensor was fabricated in the end. The experimental results showed that the DNA biosensor can detect the Avian Influenza gene sequences simply and fastly by using 2-nitroacridone as electrochemical indicator.(4) CoTe nanoparticles was synthesis by hydrothermal conditions, and then was mixed with gold nanoparticles and chitosan. Then the new-style DNA biosensor was fabricated and researched by EIS and using [Co(phen)3]³⁺ as electrochemical indicator, respectively. The experimental results showed that the DNA biosensor can detect the Avian Influenza gene sequences successfully, and compared to the two electrochemical methods, EIS is simpler and faster.