| Sequence-specific detection of DNA targets associated with genetic or pathogenic diseases and forensic applications has become increasingly important in molecular diagnostics. Nowadays, more and more interest in electrochemical methods for hybridization detection arises from the high sensitivity, low cost, and their compatibility with micro fabrication technology. This thesis is divided into six chapters:In the first chapter, the principle and classification of DNA biosensor was introduced. Research status of DNA biosensor were reviewed. This article described mainly the research status of DNA electrochemical biosensor and DNA machine.Chapter 2, this thesis discusses a novel way based on the use of biotin-avidin and DNA-modified Au nanoparticles for amplification HRP (horseradish peroxidase) to catalysis OAP - H2O2 system, Using biosensors for detecting DNA-modified Au nanoparticle amplification. First, we prepare the gold nanopaticles and combine the gold nanopaticle with two kind of DNA (SA and S1 ).After the formation of S1-Au- SA-bio, the specificity interaction enable HRP to connect to the surface of Au. We discuss the preparation condition of the Au nano-particles-HRP amplification of the DNA biosensor. The Cyclic voltammetry experiment and differential pulse voltammetry confirm the linear relationship between concentration of target DNA (T1) and electrical signal. We use these data to show effect of nano-Au to amplify the effort of HRP catalyze the reaction system of OAP - H2O2 .Chapter 3, on the basis of chapter 2, this DNA sensor was fabricated using a"sandwich"detection strategy, involving two kinds of capture probes DNA immobilized on glassy carbon electrode (GCE), and hybridization with target DNA sequences, which further hybridized with the reporter DNA loaded on the AuNPs. The AuNP contained two kinds of DNA sequences, one was complementary to the target DNA, while the other noncomplementary sequence was linked with horseradish peroxidase (HRP) and alkaline phosphatase (ALP), respectively. Enhanced detection sensitivity was obtained where the AuNPs carriers increased the amount of enzyme molecules bound per hybridization. Electrochemical signals were generated from the enzymatic products produced from the substrates catalyzed by HRP and ALP. Under optimal conditions, a 33-mer sequence could be quantified over the ranges from 1.5×10-13 M to 5.0×10-12 M with a detection limit of 1.0×10-13 M using HRP-AuNP as labels, and a 33-mer sequence could be quantified over the ranges from 4.5×10-11 M to 1.0×10-9 M with a detection limit of 1.2×10-11 M using ALP-AuNP as lables.Chapter 4, one circular DNA component is generated by the hybridization of short nucleic acids with the 3' and 5' ends of single-stranded DNA chains. A contractile DNA machine (CDM) has been built by means of crosslinking of circular DNAs into nanowires. The machine is powered by DNA and can be operated between contracted and extended states. This device has potentials in many applications such as targeted medicine delivery, gene delivery, and in-cell cargo transportation.Chapter 5, this DNA machine has been built by means of the change of PH. It is generated by the hybridization of two short nucleic acids with the 3' and 5' ends of single-stranded DNA chains. Which is twice longer than others. When HCl is added to the reaction system, fluorescence emission is lower, fluorescence emission will higher by adding NaOH. So, changing of PH perform an open-close movement in this DNA machine. DNA was adsorbed by graphene oxide nanosheet (GO-ns) and it has the ability for molecular probing in living cells. This device has potentials in many applications such as cell detection.At last, it was summarized for the whole thesis. |
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