Development Of Electrochemical DNA Biosensors Based On Electrochemical Impedance Spectroscopy

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. The detection of specific base sequences in human, viral and bacterial nucleic acids is becoming increasingly important in several areas, with applications ranging from the detection of disease-causing and food-contaminating organisms to forensic and environmental research. 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 a broad prospect of application in clinic examination of inherited diseases and drug screening.The impedance is a complex quantity reflecting the resistive, capacitive and inductive properties of the system under test and it can offer a lot of information about the electrode interfacial properties such as electronic transport resistance and double-layer capacitance. So electrochemical impedance has proved to be a powerfuland convenient tool for investigating electrode process and is a widely used and effective way to study the interface properties of the modified electrode. So it also has been used in DNA electrochemistry biosensors. And the electrode interfacial properties' differences of ssDNA and dsDNA have been detected by the frequency dependent method. Electrochemical impedance spectroscopy (EIS) even has been deemed to be the most suitable technique to evaluate the effects of mismatches on the electronic and electron-transfer properties of DNA.The combination of electrochemical impedance measurement with the event of Watson-Crick base-pairing interaction makes them excellent candidates for DNA sensors with high sensitivity and selectivity. This dissertation focuses on fabricating novel electrochemical DNA biosensors based on electrochemical impedance spectroscopy (EIS), thus developing a sensitive, sequence-specific and quantifiable gene detection method, and establishing the bases for application of electrochemical DNA biosensor to clinic diagnose.The dissertation includes five parts:Chapter 1 The review of DNA biosensorFirstly, we introduce the composition of a DNA biosensor and its classification. Secondly, emphatically review the operational principle, application and development trends of electrochemical DNA biosensor. Immobilization method of ssDNA on electrode, hybridization and signal conversion process are included. At last, impedance-based DNA biosensor and DNA biochip is introduced.Chapter 2 Electrochemical Impedance Detection of DNA Hybridization Based on the Formation of M-DNAA new selective and sensitive biosensing strategy for electrochemical impedance spectroscopy (EIS) measurement of DNA hybridization based on the Formation of metallized double-stranded DNA (M-DNA) is described. The detection approach relied on the doping of nucleic acid probes as the solo counter anions within electropolymerized polypyrrole (PPy) film onto a carboxylic group-functionalizedmulti-walled carbon nanotubes (MWNTs-COOH) modified electrode and monitoring the impedance changes provoked by the metallation of helix DNA after hybridization.. As a consequence of hybridization and the formation of M-DNA, significant changes in electrochemical impedance values (both in real component Z_re and imaginary c...