A colorimetric multilayer sensor for discriminating red wine and green tea by measurement of antioxidant activity

Natural polyphenols are important antioxidants closely associated with the health benefits of consuming plant-derived beverages. Herein, we report a simple yet sensitive multilayer sensor based on the colorimetric odor reaction between polyphenols and Fe. The sensor was fabricated by alternative assembly of a chitosan layer, Fe complexes and an alginate sodium layer on filter paper modified with a TiO membrane. After five times repeated assembly, the resultant sensor achieved good super-hydrophobicity, and together with the specific affinity of chitosan, polyphenols in aqueous samples can be pre-concentrated on the surface of the sensor, leading to improvement of the sensor sensitivity. The detection limits for model polyphenols gallic acid and tannic acid were 1.2 μM and 0.2 μM with a wide linear range between 2 μM and 6.1 mM, and between 2.3 μM and 5.2 μM, respectively. The colorimetric multilayer sensor was further applied to discriminate plant-derived drinks including 5 red wine samples and Chinese green tea samples. Statistical analysis including HCA and LDA showed that it realized successful discrimination within five closely similar red wines and five Chinese green teas of different quality grades. The sensor presented here can serve as a cheap, convenient and simple "electronic tongue" for real-time discrimination of plant-derived drinks of different brands and/or quality grades.