Development of potentiometric biosensors for determination of DPPH, FRAP and FCR antioxidant capacities and investigation of potentiometric working conditions

In this thesis study, it is aimed to develop fast, low-cost, and sensitive potentiometric biosensors as an alternative to existing classical methods in the determination of antioxidants, which are very important for human health and scavenge the effects of free radicals, which are highly unstable molecules that are released as a by-product as a result of reactions in our body. For this purpose, potentiometric biosensors have been developed separately for DPPH radical scavenging test, total phenolic test (FCR), and Iron (III) reducing power tests (FRAP). The measurability of antioxidant activity was investigated by determining the properties that characterize the potentiometric performance of each developed biosensor, such as selectivity, reproducibility, detection limit, linear operating range and response time. The optimum membrane composition for the developed DPPH•-selective PVC membrane biosensor was determined as 17.5% ionophore, 45.0% PVC, 37.5% dibutylphthalate. The biosensor's R2 value and detection limit were 0.9984 and 12.75 mg L-1 respectively, in the concentration range of 18.75 – 300 mg L-1 of DPPH• radical solution. The optimal membrane composition ratio for the FCR-selective PVC membrane biosensor was determined as 5.0% Gallic acid, 30.0% PVC, 65.0% dibutylphthalate. The biosensor's R2 value and detection limit were 0.9986 and 0.022 mol L-1 respectively, in the concentration range of 0.031 - 0.5 mol L-1 of FCR solution. The optimal membrane composition ratio for the FRAP-selective biosensor was determined as 7.0% iron(II)-quercetin complex, 34.0% PVC, 59.0% BEHS. The biosensor's R2 value and detection limit were 0.9994 and 8.0 × 10-6 mol L-1 respectively, in the concentration range of 1.0×10-5 – 1.0×10-1 mol L-1 of Fe(III) solution. The developed biosensors were successfully applied to plant samples and antioxidant determination was carried out with very high recoveries.