Study On Electrochemical Impedance DNA Biosensor Based On DNA Simulated Enzyme Signal Amplification

DNA is the carrier of genetic information, which is the most important material that can affect the genetics and health of human, the specificity of DNA is great significance in the diagnosis of diseases such as cancer, therefore detection of DNA is a focus. microRNA (miRNA) play an important role in gene regulation, embryonic differentiation, hematopoiesis, and a variety of cancers, the change of the miRNA expression can play the role of oncogene and tumor suppressor genes, which is a kind of potential tumor markers, so the detection of miRNA has attracted widespread attention. High-sensitive and high-selectivity detection of DNA and miRNA for genetic screening, early diagnosis and treatment of genetic diseases has very important significance. So far, there are many ways to detect DNA and miRNA, among the sensing technologies, electrochemical detection method is sensitive, fast, and the advantages of low cost and low energy consumption, which is favored widely by researchers.Under normal circumstances, in a sample the target DNA and the target miRNA in content are relatively low, therefore, Therefore, more and more effects have been focused on the amplify analysis of DNA by signal amplification strategies in order to enhance the sensitivity of DNA biosensors. Nano-materials have caught more and more attention because of their small sizes, large specific surface area, as well as good biocompatibility. Based on their unique physical and electrochemical properties, two kinds of electrochemical DNA biosensors with high performance fabricated by using gold nanoparticles (AuNPs) were achieved. This paper is consistsed of the following three chapters: Chapters1:IntroductionFistly, we briefly summarize the DNA biosensor, including its principle and classification of DNA biosensor. Then we emphatically review the principle, classific-ation, fixation method of DNA probe, the application of electrochemical DNA biosensors and AC impedance technology. Secondly, artificial enzymes and the application of gold nanoparticles in electrochemical DNA biosensors was introduced. Finally, the background, research ideas, purpose and contents of this paper are described. Chapters2:Impedance method to detect the target DNA Based on signal amplification of the DNAzymeWe prepare a high sensitive electrochemical DNA biosensors for detection specific sequence of DNA, which based on signal amplification of hairpin DNAzyme, The stem of the capture probe is compose of G-riched DNA sequence. In the presence of the target DNA, G-quadruplex DNA can be free from the capture probe. G-quadruplex are foure-stranded DNA structure stabilized by coordination cation, e.g., K+, K+-stabilized G-quadruplex (with hemin as cofactor) exhibit superior peroxidase-like activity and effectively accelerate the redox reaction rate of H2O2/4-Chloro-1-naphthol (CN) system. Through the biological catalysis oxidation of CN, generated insoluble oxidation product will deposite on the electrode, the precipitation were characterized by electrochemical impedance spectroscopy, We found that evident electrochemical impedance spectroscopy response signal value were appear, the sensor can direct detection hybridization of DNA.Chapters3:Sensitive Impedimetric Detection of DNA Using a Hairpin Probe Based on DNAzyme-Functionalized Gold Nanoparticle Tag-Initiated Deposition of an Insulating Film on Gold ElectrodeA kind of high sensitivity, sandwich type of electrochemical DNA biosensors is successfully prepared. Double DNA modified DiDNA/AuNPs-hemin conjugates was successfully prepared, In the presence of the target DNA, the DiDNA/AuNPs-hemin conjugates will successfully be introduced electrode. DNAzyme can catalytic redox reaction of H2O2/CN system, generating insoluble precipitate, and insoluble precipitate will adsorb on the electrode surface, which can hindered the electron transfer between [Fe(CN)6]3-/4-and the electrode, result in produce a very big impedance response signal value and achieve the signal amplification. Due to the effect of multiple load of the AuNPs, the addition of conjugates can form more G-quadruplex/hemin structure on the surface of electrode, produce greater impedance response signal values. the sensitivity of the detection DNA is higher. meanwhile the sensor can be used for the detection of DNA base mismatch, the sensor has advantages of the very good selectivity and reproducibility. Chapters4:Sensitive Impedimetric Detection of MicroRNAs Using a Hairpin Probe Based on DNAzyme-Functionalized Gold Nanoparticle Tag-Initiated Deposition of an Insulating Film on Gold Electrodewe present an electrochemical sensor along with a DNAzymes induced biocatalyzed precipitation that enables amplified impedance detection of miRNA. The hybridization of target miRNA to the loop domain opens the stem of the hairpin, DNAzyme-functionalized gold nanoparticles were introduced electrode. DNAzyme sensor were used as the catalyst for their catalytic production of insulating film in the analyte solution containing CN and H2O2. It achieves multiple DNA enzyme strategy through load of gold nanoparticles, so as to achieve the double signal amplification, The amount of the deposited insulating materials directly correlated to the concentration of the target miRNA in solution. The sensitivity of the detection miRNA is very high, Which builds a new model for the detection of miRNA.