Study On The Biosensors Based On Aligned Carbon Nanotubes Array Electrode And Au Electrode

As the requirement of clinical diagnosis, environmental detection, modern war, legal medical examination, medicine and other fields; DNA, protein, enzyme separation and analysis have taken a more and more important role. The testing requires the development of easy-to-use, fast, efficient, sensitive, selective, inexpensive, miniaturized devices. In this field, many biological technologies emerged and found their applications. But among them, electrochemical biosensors can combine with electronic techniques, have the advantages of being cheap, sensitive, reliable, and then has been one of the hot topics in the fields of medicine and biochemistry.Aligned carbon nanotubes (ACNTs), as one kind of the carbon nanotubes (CNTs), offering more advantages such as high electrical conductivity and high specific surface area. So ACNTs has been developed as one kind of the new ideal electrode material for biosensors, the high specific surface area could fix more DNA and proteins. Through bond formation, ACNTs can fix on the electrodes with the biomolecules, and have wide application prospects in the electrochemical analysis in the future.Electrochemiscal Impedance Spectroscopy (EIS) is a useful technique for the characterization of electrochemical systems, and the double layer capacitor, solution resistance, electronic transfer resistance and other electrode-solurion interfacial electrochemical characteristics can be distinguished. So it could imply in the electrochemical processes analysis, and it has the merits of label-free, fast and sensitive.The objective of this study is to develop novel biosensors with different electrode materials, biomolecules and electrochemical methods, to analyze DNA and enzyme. We functionalized ACNTs modified electrode and used to detect DNA hybridization in homogeneous solution based on the host-guest recognition. Besides, we modified Au electrode to detect the caspase-3 by electrochemical impedance spectroscopy without label. These methods simple, fast and cheap, it could offer a new method to detect DNA, protein and enzyme.Chapter 1:IntroductionFirstly, the chapter introduced the development of electrochemical biosensors, including the purpose, principle and various methods. Then we review the aligned carbon nanotubes and guest-host recognition and the applications in the biosensors. At last, we pointed out the purpose and significance of the dissertation.Chapter 2:β-cyclodextrin derivant functionalized aligned carbon nanotubes and its application for electrochemical DNA sensingHerein, we functionalized the aligned carbon nanotubes (ACNTs) electrode with a new kind ofβ-cyclodextrin (β-CD) derivant through the diazotization reaction, and the resultingβ-CD/ACNTs electrode was appiled to detect the DNA hybridization in homogeneous solution ground on the host-guest recognition. In our sensing protocol, for realizing the homogeneous phase-based DNA hybridization, a special DNA probe was designed in a stem-loop structure with the both ends modification, which was called as dually-labeled DNA probe (DLP). One end of the DLP was labeled with dabcyl as the guest molecule toβ-CD, while the other end was labeled with CdS nanoparticle as electrochemical marker to indicate DNA hybridization occurrence. In the absence of target DNA sequence, the DLP will keep its hairpin structure in the solution phase and can not be captured onto theβ-CD/ACNTs electrode. But in the presence of its complementary sequence, the DLP could open its stem-loop structure to form a double-stranded DNA (dsDNA) with target DNA, and then the dsDNA was captured onto the P-CD/ACNTs electrode because of the guest-host recognition betweenβ-CD and dabcyl. So the hybridization lead to the noticeable transformation in the DLP's structure, and only the dsDNA could be captured onto the P-CD/ACNTs electrode. Hence the electrochemical signal from the CdS nanoparticles-dsDNA/β-CD/ACNTs was measured. Under the optimized detection conditions, the proposed sensing method could give a high sensitivity with the detection limit of 5.0×10-13 M, and also a high selectivity for the sequence-specific DNA analysis.Chapter 3:A new method to detect the caspase-3 by electrochemical impedance spectroscopy without labelIn this paper, a new method was carried to detect the caspase-3 by electrochemical impedance spectroscopy without label. Firstly, the peptide (GDGDEVDGC) was immobilized on the Au electrode by self-assembly. According to the poor electro-transfer, large resistance can be obtained. After that, the caspase-3 cleaves after the aspartate residue (D), and then the resistance minished owed to the better electron-transfer. We can detect the caspase-3 through cyclic voltammetry and electrochemical impedance spectroscopy. The results show that within the narrow caspase-3 concentration from 5×10-5 to 5×10-3μg/mL, the resistance was linear to the caspase-3 concentration, and the correlation coefficient is 0.999. This assay is simple and convenient for it is label-free, and we can perform this proposed method in the future work.