Fabrication Of Electrochemical DNA Biosensors Based On Hairpin DNA And Nanomaterials

As the rapidly development of the DNA biosensor, the fabrication ofDNA biosensor with high sensitivity and selectivity has attract muchattention of the reseachers. In this work, we utilized harpin DNA probe andthe uniqueproperties of nano-materials to fabricateseveral sensitive, novel and exactDNA electrochemical biosensors successfully. The dissertation includes fourchaptersasfollows:Chapter I: A review is given on the introduction of electrochemical DNAbiosensor, research progress, hairpin DNA and application ofnanomaterials in DNA biosensor.Chapter II: We fabricated a sensitive label-free electrochemical hairpinDNA biosensor based on graphene-thionine composite (GR-Thi). The Thiwas noncovalently bound to the GR sheet through π-π stacking and theGR-Thi composite was dropped on the surface of the glassy carbonelectrode (GCE) firstly. Subsequently, the gold nanoparticle (Au-NPs) wasanchored to the surface of Thi–GR by the chemisorption of the aminegroups of the THi and the opposite charged adsorption. Then thethiol-modified hairpin DNA was immobilized on the electrode surfacethrough the Au-S binding. Differential pulse voltammetry (DPV) wasemployed to monitor the hybridization of DNA by measuring the changesof the peak current of thionine. The biosensor exhibited good sensitivityand could recognize target DNA in the presence of large amounts ofmismatched sequences, which indicated that the biosensor had high selectivity.Chapter III: We fabricated an electrochemical hairpin DNA biosensorbased on Au-NPs modified electrode and enzyme amplificatiom protocol.The thiol-modified hairpin DNA was immobilized on the Au-NPs modifiedelectrode surface through the Au-S bonds. In the design of the biosensor,the conformational change of the hairpin before and after hybridization, thespecificity combination of biotin and streptavidin, and the signalamplification ability of enzyme (horseradish peroxidase, HRP) werecombined to detect the target DNA sequences. The hybridization detectionwas monitored by DPV, and the result showed that the DNA biosensor hadhigh sensitivity and selectivity.Chapter Ⅳ：We fabricated an ultra-sensitive electrochemical hairpinDNA biosensor based on Au-NPs modified electrode and HRP-streptavidincapped Au-NPs (HAS) conjugates for signal amplification protocol. Basedon the principle of the work in Chapter III, larger amouts of enzyme wereintroduced in the biosensor through the HAS conjugates linking to theelectrode, which makes the signal ampilificated significantly. It wasnoticeable that the Au-NPs dually amplified the signal in this biosensor.The hybridization detection was monitored by DPV, and the results showedthat the DNA biosensor had high sensitivity. Furthermore, this biosensoralso demonstrated its excellent specificity for single base mismatchedDNA.