Paper microzone plate based on DPPH as a simple colorimetric assay of the total antioxidant content of herbal extracts.

The human body needs an antioxidant-rich diet that comes from foods, beverages, and herbal products to support the physiological antioxidant systems. Thus, the development of an analytical tool for a simple assay of the total antioxidant capacity (TAC) of the rich antioxidant samples is crucial. The current work demonstrates a simple colorimetric assay of TAC of the herbal extract on the paper microzone plate (PµZP) that was constructed in the 70-well of patterned paper using the screen printing technique. The PµZP was constructed by immobilizing DPPH (2,2-diphenyl-1-picrylhydrazyl) onto 70-well of PµZP as a sensing zone for colorimetric detection. The purple-sensing zone exhibited a good response to gallic acid (GA), by producing slightly gray to pale yellow color that can be captured using a scanner and then analyzed using the ImageJ program. The paper-based sensor showed a linear response toward GA at 0.05-0.6 mM (r = 0.9895), reproducible response (RSD < 4%), and accurate measurement with 91 to 106% recovery for measuring TAC of herbal extract, presented as mM gallic acid equivalent and showed a good agreement with the standard DPPH method. The results suggested that the proposed method can be applied for simple TAC measurement in the herbal extract. © Association of Food Scientists & Technologists (India) 2020.