Research Information System
5th ICABC, Antalya, Turkey, 4 - 07 March 2024, pp.31
The CUPRAC (Cupric Ion Reducing Antioxidant Capacity) method using bis-neocuproine copper (II) complex ([Cu(Nc)2]2+) was first developed by Reşat Apak et al., in 2004 for the determination of total antioxidant capacity1. The colorimetric CUPRAC method depends on the conversion of the slightly blue [Cu(Nc)2]2+ to yellow-orange bis-neocuproine copper (I) complex ([Cu(Nc)2]+) in the presence of a reductant (antioxidant), and many optical sensors were developed by monitoring the absorbance of cuprous-neocuproine chelate at 450 nm. In our recent studies, two new approaches for this useful chromogenic oxidant have been proposed, namely the development of enzyme-based optical biosensors as well as electrochemical sensing based on its use as a redox mediator. In the first approach, the CUPRAC reagent was integrated into enzyme-based optical biosensors2. In the first step, enzymes such as oxidase, dehydrogenase, and acetylcholine esterase (AChE) were immobilized on the silanizated magnetite nanoparticles. In the second step, enzymatic reactions were accomplished between enzyme-immobilized nanoparticles and substrate (glucose, cholesterol, acetylthiocholine, etc.). In the final step, a colorimetric reaction was realized between enzymatically produced products (for example H2O2 from oxidase enzyme, NADH from dehydrogenase enzyme, thiocholine from AChE, etc.) and [Cu(Nc)2]2+. Thus, the optical biosensor was constructed based on measuring the absorbance of the yellow [Cu(Nc)2]+ product formed at 450 nm. Using this approach, glucose, cholesterol, and lactate biosensors based on their oxidase enzymes, a glucose biosensor based on glucose dehydrogenase enzyme, and a paraoxon ethyl biosensor based on the inhibition of AChE by the pesticide were developed. In the second approach, modified electrodes have been prepared with CUPRAC-reagent for the electrochemical sensing of some compounds3. In the first step, bare electrodes such as glassy carbon, pencil graphite, and screen-printed carbon electrodes were modified with a negatively charged polymer or polyelectrolyte such as Nafion and sodium dodecyl sulfate. Then [Cu(Nc)2]2+ was modified on these electrodes through electrostatic interaction between negatively charged perfluorosulfonate groups and positively charged cupric complex. After this effective modification, the electrocatalytic activity of CUPRAC-modified electrodes was investigated for the oxidation of some compounds. Recorded cyclic voltammograms showed that the modified electrodes have a good redox couple at around formal potential of 400-500 mV vs Ag/AgCl. In the presence of a reducing analyte, the oxidation peak current of [Cu(Nc)2]2+ increased remarkably by the analyte, while the reduction peak current slightly decreased. Moreover, the oxidation potential of compounds studied at modified electrodes was remarkably shifted to more negative values compared to that at bare electrodes. These results indicate the typical electrocatalytic properties of the modified electrode. As a result, the CUPRAC reagent exhibits a good redox-mediator property. Using this approach, flow-injection-amperometric sensors were developed for the determination of H2O2, hydrazine, hydroxylamine, and total antioxidant capacity.