Equipment-free determination of ascorbic acid based on the UV-induced oxidation of 3,3′,5,5′-tetramethylbenzidine in a paper-based analysis device

Abstract

A simple, portable and cost-effective paper-based analysis device is developed for quantitative determination of ascorbic acid (AA) based on the UV-induced oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB). The method does not involve the introduction of any enzyme or external oxidants. More importantly, large equipment is not needed and only a 20 μL sample is needed for each analysis which only takes 8 min. The filter paper is pre-treated with TMB and it turns blue upon UV irradiation because TMB is a self-photosensitizer. The phenol hydroxyl groups of AA can inhibit photo-triggered oxidation resulting in a lighter blue color. The color signal is captured using a smartphone and analyzed using color analysis software. A series of factors that affect the performance of the device are investigated, including the concentration of TMB, buffer pH, channel selection, and irradiation time. The analytical performance is evaluated, and the results show that the method has a wide detection range of 0.05–1.0 mmol L⁻¹ as well as a high selectivity and reproducibility. The proposed method is applied for assaying AA in beverage samples and a VC tablet, and the results correspond to those obtained using the UV method. The results of the recovery test of human serum indicate that the proposed method is feasible in biological samples. This device is easy to fabricate, and convenient to store and transport. It is a truly portable device which has great potential in the on-site assay.