As antioxidant consumption is an important way to combat oxidative stress-related diseases, there is a continued interest in developing sensitive, simple and low cost antioxidant capacity assessment methods. In this regard, a novel biopolymer-based colorimetric sensor was designed for total antioxidant capacity (TAC) assessment. Carrageenan polysaccharide was chosen as a building brick of the prepared biopolymeric film. Owing to the anionic sulfate groups of the carrageenan biopolymer, the film exhibited cation exchange properties. The proposed optical sensor was shown to immobilize copper(II)-neocuproine (Cu(II)-Nc) chromogenic reagent cation onto a carrageenan film via sulfate groups. When the Cu(II)-Nc reagent immobilized on the biopolymer film was reduced with antioxidants, a Cu(I)-Nc colored chelate complex would form on the film showing a high absorbance at 450 nm. A number of antioxidants were tested by the proposed sensor so as to compare their trolox-equivalent antioxidant capacities with those found by the original solution-based cupric reducing antioxidant capacity assay, revealing that the biopolymer-immobilized Cu(II)-Nc reagent was still effective in oxidizing antioxidants. The proposed sensor was validated to measure the TAC values of synthetic mixtures, fruit juices and medicinal plant extracts. As opposed to the solution-based method, the sensor worked well in turbid solutions without pretreating samples.