Amperometric sensor for total antioxidant capacity measurement using Cu (II)-neocuproine/carrageenan-MWCNT/GCE

Determination of total antioxidant capacity (TAC) in foods is very important for combating oxidative stressinduced diseases. For this purpose, an amperometric sensor was developed for TAC determination by manufacturing a new electrode consisting of a copper(II)-neocuproine (Cu(II)-Nc) and carrageenan-multi-walled nanotube suspension functionalized on a glassy carbon electrode, named as Cu(II)-Nc/Car-MWCNT/GCE. Cyclic voltammetric studies showed that the modified electrode exhibits a very well-formed reversible redox couple for the Cu(II)-Nc/Cu(I)-Nc complex. For amperometric sensor preparation, the Cu(II)-Nc cationic chelate was electrostatically retained on the electrode with the anionic groups of Car (a sulfated biopolymer of low cost) and immobilized on the surface. Cu(II)-Nc was reduced to Cu(I)-Nc on the electrode with the addition of antioxidants under constant potential, thereby functioning as an electron-transfer mediator. Thus, the individual antioxidant compounds were not measured at their own peak potentials but were indirectly measured at a common potential through their ability to reduce cupric-to-cuprous neocuproine. The reoxidation current of Cu(I)-Nc showing a proportional increase with antioxidant concentration was recorded, resulting in increased sensitivity and selectivity. This anodic current intensity of Cu(I)-Nc correlated with the total antioxidant capacity (TAC) of real samples such as plant extracts, reflecting the combined reducing ability of all antioxidants in the sample. Calibration graphs of antioxidants were obtained by optimizing the working conditions. The current intensity of Cu (I)-Nc arising from trolox varied linearly with concentration in the range of 4.98-84.39 mu M. The limit of detection and limit of quantification values for trolox were found to be 0.59 and 1.99 mu M, respectively. The developed method selectively responded to food antioxidants, and was not affected by potential interferent ions and molecules commonly found in foods. The TAC values of real samples such as herbal teas, plant extracts, and fruit juices were calculated and compared with those found by the conventional spectrophotometric CUPRAC method.