Research Of Biosensing Technology Based On Fuctional Nucleic Acid

Biosensor is a kind of new detection technique, with high selectivity and sensitivity, perfect stability, low cost and fast detection in complicated system, and so on. The current biosensors have been reported in hundreds of species and new types of biosensors are emerging, equipment performance continuously improving, have made a wide range of applications in health care, food hygiene, environmental monitoring, defense and security.This research paper is concerned with a number of problems for the current development of sensor technology. The detailed materials are described as follows:(1) A simple, rapid and highly sensitive photochemical sensor based on enzyme-catalyzed signal amplification has been proposed and applied to detect nucleic acid. So a fluorescence-quenched probe has a fluorescein (FAM) fluorophore and a carboxytetramethylrhodamine(TAMRA) quencher-labeled tail at the 3'-end. In the presense of target DNA, the fluorescence-quenched probe hybridizes with the target nucleic acid forming hybrid complex. So ExoⅢis able to hydrolize the fluorescence-quenched probe causing the separation of fluorophore and quencher and emitting fluorescence from FAM. Furthermore, signal amplification can be realized via the reutilization of target DNA.The developed strategy could quantitatively determine the target DNA in the dynamic range of 50 pM to 750 pM with the detection limit of 1 pM (in Chapter 2).(2) Carbon nanotubes (CNTs) have valuable applications in electrochemical biosensors due to large aspect ratio, better chemical stability, excellent electrical conductivity and high electrocatalytic activity. Based on these advantages, we developed an electrochemical strategy based on strand displacement reaction coupling with the CNTs as electrochemical labels for the detection of the specific sequence DNA. In the presence of the target DNA, the DNA hybridization between the target DNA and the DNA probe wrapped on the nanotubes,could actively remove DNA probe from the MWNTs surface and induce the precipitation of MWNTs onto the 16-mercaptohexadecanoic-acid-modified Au electrode substantially mediating heterogeneous electron transfer between bare gold electrode and redox species in solution phase. In the absence of the target DNA, the MWNTs wrapped by ssDNA did not adsorbe on the 16-mercaptohexadecanoic-acid self-assembled monolayer (SAM), and thus reducing the background current. The experiment results demonstrated that the electrochemical signal of the electrode was correlated with the concentration of target DNA in the range from 10 pM～100 nM with a detection limit of 5 pM (in Chapter 3).(3) Heavy metals in our environment can hardly be degradated. Heavy metal accumalation in human via various approached does harm to human beings, even endangering our lives when seriously. In this experiment, coupling thymine-Hg2+-thymine (T-Hg2+-T) coordination chemistry with the CNTs as electrochemical labels, we developed a novel electrochemical strategy for the determination of Hg2+. The effect of concentration of salt ion, the interference of coexisting ions with Hg2+ and temperature of strand displacement reaction on the performance of the assay were investigated. According to the experimental results, we know that the Hg2+ could be determined in the range of 20 nM～10μM with a detection limit of lOnM. (in Chapter 4).