Fabircaiton Of DNA And Hg²⁺ Biosensors Based On Gold Inanomaterials

In this work, we used the unique properties of nano-materials withmodern electrochemical technology, optical technology, nucleic acidhybridization, and successfully fabricated two simple, sensitive and novelDNA electrochemical and optical biosensors. It has been reported thatHg2+possesses a unique property to specifically bind to two DNAthymine bases and promote T–T mismatches to form stable base pairs,and then we describe the fabrication of an ultrasensitive Hg2+electrochemical biosensor based on the interaction of T–Hg2+–T. Thepractical application of the proposed sensors was also assessed. Thedissertation includes four chapters:Chapter I: A review is given on the introduction of electrochemicalDNA biosensor, optical DNA biosensor and Hg2+biosensor, researchprogress, and nano-materials application in these biosensors.Chapter II: We prepared a label-free electrochemical DNA biosensorbased on a glassy carbon electrode modified with gold nanoparticles(Au-NPs) and Graphene-Methylene blue (Graphene-MB) compositenanomaterials. Then DNA probes (HS-DNA) were immobilized on thesurface of the AuNPs/Graphene-MB/GCE via Au-S bond. Under optimal conditions, the decline of the peak currents of methylene blue (ΔI) waslinear with the logarithmic of target DNA. We fabricated a simple andhigh sensitivity DNA electrochemical biosensor.Chapter III: In this study, we designed a fluorescence resonanceenergy transfer system containing gold nanorods (AuNRs) andfluorescein (FAM) for the detection of hepatitis B virus DNA sequences.When FAM-tagged single-stranded DNA (FAM-ssDNA) was added intothe AuNRs suspension, leading to a fluorescence resonance energytransfer (FRET) process from FAM to AuNRs and the fluorescenceintensity of FAM was consequently quenched. When complementarytarget DNA was added to the complex solution, a further decrease influorescence intensity was observed because of an increased FRETefficiency. Under optimal conditions, the decline of the fluorescenceintensity of FAM （ΔF） was linear with the concentration of thecomplementary DNA from0.045to6.0nmol L-1and the detection limitwas as low as15nmol L-1(signal/noise ratio of3).Chapter Ⅳ: In the assay, we describe the fabrication of anultrasensitive electrochemical biosensor for the determination of themercury (II) ion (Hg2+) in aqueous solution. The biosensor is based on aglassy carbon electrode (GCE) modified with multi-walled carbonnanotubes (MWCNTs) and gold nanoparticles (Au-NPs). In the presenceof Hg2+, the probe DNA can hybridize with the target DNA to form duplex DNA via the strong and specific binding of Hg2+by two DNAthymine bases (T–Hg2+–T). Differential pulse voltammetry was employedto investigate the hybridization process and measure the changes in peakcurrent intensity of intercalated adriamycin in the presence of differentconcentrations of Hg2+. In addition, the biosensor exhibits goodselectivity, stability and reproducibility.