Development Of Highly Sensitive Electrochemical DNA And Aptamer-Based Biosensors

In this thesis, according to different target analyte to build several different new type of electrochemical biosensors based on DNA and aptamer. They have been widely recognized as highly promising tools for specific sequences of DNA fragments, thrombin and adenosine triphosphate (ATP). In addition, a simple electrodeposition method was used to fabricate various palladium nanostructures modified electrodes. Further investigation of the modified electrodes showed their high electrochemical activity toward methanol oxidation. The main contents are listed below:1. Enzyme-free and ultrasensitive electrochemical detection of nucleic acids was developed by target catalyzed hairpin assembly followed with hybridization chain reaction. Firstly, the thiol group functionalized immobilized probe (denoted as IP) is immobilized onto the gold electrode surface. When the target appears, it hybridizes with the hairpin structure of IP and free the target DNA. The released target DNA can participate in the next hybridization process with more IP. With the ingenious combination of target catalyzed hairpin assembly and HCR strategies, we can achieve an enzyme-free and dual signal amplification for DNA detection. It could only obtain a detection limit of about10-16M.2. A good selectivity and feasibility strategy was based on gold nanoparticles differential pulse anodic stripping voltammetry (DPASV) method and aptamer to detection of thrombin. Thrombin binding aptamers (1μM) were respectively modified with the novel gold nanoparticles (AuNPs) and magnetic beads to form a sandwich assay. The detection system was based on a sensitive differential pulse anodic stripping voltammetry (DPASV) method for the detection of Au tracers, which were obtained by dissolving the sandwich structure. We report a good selectivity and feasibility method for electrochemical analysis of thombin. It could only obtain a detection limit of10-14M.3. Homogeneous electrochemical aptamer-based ATP assay with signal amplification was developed by exonuclease Ⅲ assisted target recycling. A hairpin-aptamer probe is ingeniously designed, which consists of an aptamer sequence for ATP that is caged in the duplex structure of the stem and a ferrocene tag labeled at the3’terminus. In the presence of ATP, the hairpin-aptamer probe reconfigures to the active G-quadruplex structure that binds ATP. As a result, Exo Ⅲ hydrolytically digests the3’end strand, resulting in the release of ferrocene labeled mononucleotide and subsequently the dissociation of ATP. This process results in the recycling of the ATP analyte, which is then free to form a complex with another hairpin-aptamer probe, and thus the autonomous cyclic formation of the free ferrocene-labeled mononucleotide is activated. This method could avoid the complex operation to the heterogeneous reaction. It could only obtain a detection limit of1nM.4. A simple one-step electrodeposition method was used to fabricate various palladium nanostructures on gold electrodes in a solution containing HC1and28.2mM PdCl2.A novel Pd nano-material surface consists of nanostars were synthesized by changing electrochemical deposition potentials and deposition times. Further investigation of the Pd nano-materials electrodes showed their high electrochemical activity toward methanol oxidation.