Development of a novel cysteamine-single walled carbon nanotube modified tyrosinase based enzyme biosensor system and investigation of some tyrosinase inhibitors

In the thesis, it was aimed to develop a modified tyrosinase biosensor of cysteamine / SWCNT / glutaraldehyde to determine kojic acid, a tyrosinase inhibitor. The kojic acid assay was performed in the presence of catechol, the substrate of the enzyme, based on competitive inhibition. In biosensor design, self assembled monolayer (SAM) formation on gold electrode surface was performed with cysteamine. After this modification, single walled carbon nanotubes were attached to the electrode surface and crosslinked with glutaraldehyde by tyrosinase binding. Determination of kojic acid in the presence of catechol with tyrosinase biosensor was performed between (-0.2) & (+0.6) V potential with differential pulse voltammetry. Measurements were performed in K3[Fe(CN)6] and the principle of inhibition of tyrosinase conversion of catechol o-benzoquinone with kojic acid. The characterization studies of the modified electrode used in the designed biosensor have been carried out. For this purpose, optimization of the amount of enzyme, cysteamine incubation time, optimization of SWCNT amount and SWCNT incubation time and finally optimization of glutaraldehyde concentration were performed. Temperature, pH, buffer concentration effect was examined for optimization studies for working conditions. In studies to characterize the tyrosinase biosensor, linear range, reproducibility, the effect of different species on the biosensor response and the individually responses of the other species are examined. At the end of these studies, the optimum amount of enzyme was determined as 0.58 U / μL, the incubation time of cysteamine was 9 hours, the SWCNT amount was 1 mg / mL, the incubation time of SWCNT was 4 hours and the volumetric glutaraldehyde concentration was 2.5%. 50 mM pH 7.0 potassium phosphate buffer was used as the buffer solution in the tyrosinase biosensor. The working temperature is 25 ° C. The linear working range of the tyrosinase biosensor was determined to be 10 - 150 μM.