The Development Of Electrochemical DNA Biosensor

Up to now, the DNA detection has become more and more important in diagnosis and the treatment of genetic disease, as well as as the identification of genomic sequence variations. In order to detect the mismatched DNA, in the present work, the electrochemical methods were used to study the DNA biosensor. In order to monitor DNA/DNA interaction at solid/solution interface, we studied the immobilization of DNA and the DNA/DNA hybridization kinetics on the electrode/solution interface; some new methods have also been developed to detect DNA targets. The details can be seen in the following:1. The hybridization of immobilized oligonucleotides probe strands with solution phase targets is the underlying principle of microarray-based techniques for the analysis of DNA variation. A label-free method of electrochemical impedance spectra (EIS) was used to study the kinetics of DNA/DNA hybridization and then some important kinetic parameters, such as the association rate constant (K_on), the dissociation rate constant (K_off) and the affinity rate constant (K_A), for perfect matched DNA hybridization, were obtained. 2. A new nanohybrid of carbon nanotubes-hexadecyl trimethyl ammonium bromide (CNTs-HTAB) was prepared based on solid-state mechanochemical reaction for label-free DNA detection. It was found that CNTs-HTAB modified electrode could greatly enhance the immobilization of ssDNA by electrostatic attraction and decrease the potential difference between the oxidation of guanine (G) and adenine (A) compared with that on bare glassy carbon electrode. The higher ssDNA immobilization ability and smaller potential difference between the oxidation of G and A on CNTs-HTAB modified electrode lead to an amplified the potentiometric stripping analysis (PSA) signal for label-free ssDNA detection by oxidizing both G and A synchronously. The signal amplification could then lead to a low ssDNA (15-mer) detection limit of 2×10^-11M. The DNA hybridization could be performed successfully by controlling the accumulation time of DNA probes to avoid both the nonspecific adsorption of target DNA and the overlap between different DNA probes.3. Based on the conformational changes of G-quadruplex/hemin complex after hybridization on Au electrode surface and the catalysis of hemin on the reduction of hydrogen peroxide, we developed a new type of DNA biosensor to detect the mismatched DNA strands selectively.