Development of electrochemical biosensors sensitive to MikroRNA-133a

In the thesis study, an electrochemical biosensor was developed for the quantitative determination of microRNA-133a (Target-miR-133a), a cancer biomarker. It is aimed to develop a sensitive, fast, cheap and practical biosensor with high sensor selectivity, designed according to the nucleic acid hybridization principle. For this purpose, a disposable, low-cost and practical pencil graphite electrode (PGE) was used. The surface of the PGE electrode was activated by electrochemical method. The anti-miR-DNA strand, the complementary conjugate of the target molecule miRNA-133a, was adsorbed to the surface of the PGE as a capture probe (cp). Anti-miR-DNA/Target-miR-133a hybridization was carried out by keeping the prepared electrode in the target molecule solution. All processes that occurring on the electrode surface were characterized by electrochemical impedance spectroscopy (EIS) at each stage. Optimization of capture tip (cp-DNA-miR-133a) concentration immobilized on the electrode surface, adsorption time, target molecule concentration and hybridization time were studied separately. Due to the strong hydrogen bonds between the capture probe and the target molecule, an increase in the charge transfer resistance of the electrode surface was observed after the molecules were hybridized. Since the initially well-conducting PGE electrode surface was covered with insulating biomolecules, the charge transfer resistance of the PGE electrode increased with adsorption of the capture probe and hybridization, respectively. In addition, the biosensor was studied in phosphate buffer (PBS) and acetate buffer (ABS) media to evaluate its applicability in different buffer environments. In the selectivity studies of the biosensor, the performance of the biosensor was tested in acetate buffer in the presence of pseudotarget molecules with different base sequences.