| Tumors, one of the most threatening diseases of the human being, plays an essential role in modern medicine. In general, tumors appear to occur when there is a problem with the dividing of cells in the body. Typically, the division of cells in the body is strictly controlled. New cells are created to replace older ones or to perform new functions. Cells that are damaged or no longer needed die to make room for healthy replacements.If the balance of cell division and death is disturbed, a tumor may form. In recent years, many assay methods and sensors as currently popular techniques are being developed for the detection of tumor-related biomarkers.This thesis studied a novel electrochemical biosensor based of aptamer and its application in assay of tumor cells and thrombin. Au nanoparticles and Hairpin were also used in this biosensor. This thesis mainly consists of the following issues:1 A novel electrochemical assay based on the aptamer and the signal of amplification of nanoparticles (NPs) was constructed for the determination of thrombin. Aptamers immobilized on the electrode and Au NPs could be assembled with the target protein to form a sandwich structure in the presence of the latter. Differential pulse voltammetry (DPV) was employed to detect the CdS NPs loaded on the surface of the Au NPs through the linker DNA, which was related to the concentration of the target protein. The assay took advantage of the amplification ability of Au nanoparticles carrying multiplex CdS NPs and the specific affinity of aptamers. Thrombin was detected in this assay in the linear range of 1.0×10?15 to 1.0×10?11 M with the detection limit of 5.5×10–16 M of target protein. In addition, the assay could be used to detection thrombin in real samples with high sensitivity and good selectivity. 2 A novel electrochemical cytosensing strategy was constructed by using aptamer and bio bar code DNA-conjugated gold nanoparticles (Au NPs) to combine the selectivity and affinity of aptamers and the signal amplification of bio bar code DNA to allow for the sensitive detection of cancer cells. The anodic stripping voltammetry (ASV) technology was employed for the elemental detection of CdS NPs labeled on the bio bar code DNA for further assay the amount of the target cells. With the use of Burkitt's lymphoma cells (Ramos) as a model, the electrochemical method could respond down to 67 cells mL-1 of cancercells with a linear calibration range from 1.0×102 to 1.0×105 cells mL-1, showing very high sensitivity. In addition, the assay was able to differentiate between different types of target and control cells based on the aptamer used in the assay indicating the wide applicability of the assay for diseased cell detection. On the basis of these qualities, aptamer and bio bar code-conjugated gold nanoparticles could become a powerful tool for point of care diagnostics.3 Based on the extension reaction of primer 2 in the presence of the DNA polymerase, the inherent signal-transduction mechanism of the hairpin fluorescence probe, and the strand-displacement property of polymerase, an amplified fluorescence detection of cancer cells was described in this manuscript.By using magnetic bead as both the separation tool and the immobilization matrix of the aptamer of Ramos cells (CRL-1596, B-cell, human Burkitt's lymphoma), the detection of the amount of the Ramos cell with the low concentration of 100 cells mL-1 confirmed the reliability and practicality of the protocol, which reveal a good prospect of this platform for analysis. |
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