Chiang Mai Journal of Science

     In this work, a low cost and portable optical sensor using a smartphone camera for antioxidant analysis was demonstrated. A platform was designed and installed on a smartphone as an attachment for the assay solution, a macro lens, and a white LED. The proposed confi guration allowed the illumination from the white LED to pass through the solution before entering the smartphone camera. After the color of the solution was captured by the camera, the image was sent to a laptop by Bluetooth and the Red, Green and Blue (RGB) intensity values were determined using ImageJ software. The proposed platform was used to assess the antioxidant capacity of standard Trolox, gallic acid, and a range of herbal teas using 2,2’-azinobis-(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) and 1,1-diphenyl-2-picrylhydrazine (DPPH) assay, and then calculated as an IC₅₀ value. The total phenolic compounds (TPC) of these samples were also evaluated using Folin-Ciocalteu (FC) assay, and presented as gallic acid equivalents (GAE). The results of the three assays when using the smartphone were in good agreement with those from a commercial UV-Vis spectrophotometer. For the three assays, a good linearity and precision were obtained R² > 0.995, and % RSD was lower than 2% (n = 5), respectively. For FC assay, the linear range and the limit of detection were 0.0-7.0 mg/L and 0.20 mg/L, consequently.