New Nano-materials As Applied To Sensing-interface Fabrication For Electrochemical Biosensors

Electrochemical biosensor, which has been developed rapidly in recent years, is one new type of biosensors. This kind of biosensors has many superior advantages such as high sensitivity, nice selectivity, low cost and easy miniaturization, which has been widely used in clinical medical analysis, environmental monitoring and food engineering. The key aspect in the construction of the electrochemical biosensor is the immobilization procedure of biomolecules on the sensor surface. The aim of this dissertation is to develop simple and sensitive immobilization strategies of biomaterials in order to improve the performance and long-term stability of the electrochemical biosensors. The main works of the research paper are as follows:1. MnO₂ nanoparticle was synthesized by solid state reaction at room temperature and was immobilized on glass carbon electrode (GCE) by way of the film forming of chitosan (CHIT).The immobilization and hybridization of DNA on the MnO₂/CHIT film were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) method.The results indicated that the electron transfer resistance (Ret) of the electron surface was increased after the hybridization of probe DNA with target DNA.Based on this,a sensitive label-free DNA electrochemical biosensor was fabricated. The DNA biosensor showed a wide linear response to the logarithm values of Escherichia coli concentration in the range of 2.0×10^-11 mol/L～2.0×10^-6 mol/L, with a detection limit of 1.0×10^-12 mol/L.2. ZnO was synthesized by solid state reaction and was immobilized on GCE via the film forming by chitosan (CHIT). The developed ZnO/CHIT/GCE electrode was a good platform of DNA immobilization and hybridization. Under optimal conditions, the DNA biosensor showed a wide linear response to human immunodeficiency virus (HIV) gene in the range of 2.0×10^-11 2.0×10^-6 mol/L, with a detection limit of 2.0×10^-12 mol/L of complementary target.3. Adenosine aptamer was immobilized on GCE via the film forming property of chitosan (CHIT). The results indicated that the electron transfer resistance (Ret) of the electron surface was increased after the hybridization of probe aptamer with target adenosine. The response impedance change is proportional to the amount of adenosine in sample. The linear range of the signal was observed between 1.0×10-8 mol/L and 5.0×10^-6 mol/L of adenosine with 0.9990 correlation factor. This method was able to linearly and selectively detect adenosine with a detection limit of 1.0×10^-9 mol/L.4. A simple and highly sensitive electrochemical impedance spectroscopy (EIS) biosensor based on nano-MnO₂ as a platform for the immobilization of the aptamer was developed for the determination of adenosine. In the measurement of adenosine, the change in interfacial electron transfer resistance (Ret) of the biosensor using a redox couple of [Fe(CN)6]3-/4- as the probe was monitored. The change of the electron transfer resistance (ΔRet) of the biosensor was linear with the concentration of adenosine in the range from 1.0×10^-9 mol/L to 1.0×10^-6mol/L. The detection limit was 8.0×10-10 mol/L.