| Deoxyribonucleic acid (DNA) has the function of storing and transmitting genetic information. A lot of clinical diseases result from the DNA base sequences' variability, therefore the detection of specific DNA sequences can provide a reference for related disease diagnosis and treatment. DNA electrochemical biosensor is a biosensor for DNA detection using electrochemical means. Compared with the conventional DNA labeling methods, it has such advantages as simple operation, good specificity, high sensitivity, low price, etc., and can be widely applied in medicine, environment and food analysis.Aptamer is a class of single-stranded DNA or RNA sequences screened by SELEX technology. Through the specific combination with target molecules, it can be widely applied in the field of molecular recognition. The specific recognition of the aptamer can be comparable with the monoclonal antibody technology, and has special advantages compared to conventional antibodies. Aptamer electrochemical biosensor is a biosensor for electrochemical detection in advantage of the specific recognition of aptamer and target molecules. The detecting principle is similar to DNA electrochemical biosensor. With the advantages of high specificity, high affinity, high stability, target molecules diversity, and easy modification synthesized in vitro, etc., it has aroused great interest of scientists and developed very rapidly.As a kind of carbon nanotubes, aligned carbon nanotubes (ACNTs) has many outstanding properties, such as good orientation, compact arrangement, stable mechanical strength, large surface area and high electrical conductivity, etc.. Compared to conventional electrodes and general carbon nanotubes electrodes, it has unique advantages and is more conducive to fixing biological molecules due to larger surface area and the electrode functionalization. Therefore, ACNTs has been widely applied in the field of biosensors as a kind of ideal electrode material.The host-guest recognition is to take advantage of the weak non-covalent bonds between host molecules and guest molecules to form a specific functional system. As common host molecules, crown ether, cyclodextrin, calixarene and cucurbituril, etc., can bind guest molecules specifically through Van der Waals force, hydrogen bond or hydrophilic-hydrophobic interaction, etc.. With the gradual in-depth research in the field of analytical chemistry, environmental monitoring, pharmaceutical preparation and biosensors, it has developed very quickly.In this paper, we have fabricated two electrochemistry biosensors using carbon nanotubes. The first one is an aptamer biosensor with the specific recognition between thrombin and aptamers, and the second one is a DNA biosensor with the host-guest recognition between CB[7] and dabcyl group. The detection sensitivity can be improved greatly through the co-amplification of the ordered nanomaterial transducer and nanoscale markers. At the same time, the host-guest recognition can detect target DNA in the homogeneous solution, and the detection sensitivity can be improved further by increasing the hybridization efficiency.This paper consists of the following three chapters.Chapter One:PrefaceFirstly, we introduced the general situation and research progress about the electrochemical biosensors, in which the principle and application of the DNA biosensors and the aptamer biosensors were highlighted. Then we reviewed the carbon nanotubes array about its structure, properties and the application of aligned carbon nanotubes array in electrochemical biosensors. Finally, we illustrated the principle of host-guest recognition and its application in electrochemical biosensors. On this basis, we pointed out the purpose and significance of this paper. Chapter Two:A Novel Thrombin Aptasensor Based on Diazotization Functionalized Aligned Carbon NanotubesIn this chapter, we prepared a thrombin aptasensor on ACNTs with a sandwich detection mode to take advantage of the specific recognition between thrombin and two kinds of aptamers. Firstly, we chose the diazotization functionalized ACNTs as the substrate electrode, and then fixed amino-modified aptamer I to the substrate electrode surface through the amide condensation. After capturing thrombin specifically, the electrode was used to capture CdS nanoparticles-modified aptamer II, so the stable sandwich structure was built. Finally, the CdS nanoparticles on the electrode were dissolved in acid solution, and we could indirectly detect the thrombin concentration through detecting Cd2+oxidation peak current in DPV method on a mercury film electrode. This biosensor has many advantages, such as simple operation, high sensitivity with the limit detection on3.5×10-13M, good specificity and stability.Chapter Three:The Application of a Novel DNA Electrochemical Biosensor on Host-guest Recognition Using CB[7] as the Host MoleculeHerein, we prepared a DNA electrochemical biosensor on MWCNTs to detect target DNA in the homogeneous solution with the host-guest recognition between CB[7] and dabcyl group. Firstly, we prepared a dual-labeled DNA probe with dabcyl group and CdTe quantum dots, and then we chose CB[7]/MWCNTs modified glassy carbon electrode as the substrate electrode. Before the hybridization reaction, the probe DNA maintained the stem-loop structure, and CB[7] on the electrode could not capture dabcyl group due to the steric hindrance effect. But after hybridizing with target DNA, the stem-loop structure of the probe DNA would change into a straight chain structure, so that dabcyl group could be captured by CB[7] on the substrate electrode through host-guest recognition. We could indirectly detect the target DNA concentration through detecting Cd2+oxidation peak current on the electrode surface. This biosensor could raise the hybridization efficiency through the DNA homogeneous hybridization so that it could improve the detection sensitivity with the limit detection on7.0×10-13M. |
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