Preparation of a novel green optical pH sensor based on immobilization of red grape extract on bioorganic agarose membrane

•The anthocyanins of red grape were extracted.•Red grape extract is covalently bonded to a transparent epoxy activated agarose film.•The prepared optical sensor successfully applied for pH monitoring.•The sensor responds rapidly to the pH changes in a range of 1–10.

The development of a novel green optical pH sensor for a wide range pH values is described based on the immobilization of grape extract on an optically transparent agarose biopolymer. Siahe Sardasht grape is a famous variety of grape in Iran that is used for red grape juice concentrate. The anthocyanins of Siahe Sardasht grape were extracted and used as a suitable dye for the preparation of a pH optical sensor, by its immobilization on a transparent agarose film. In an optimized coupling, pH of 10 and a dye concentration of 100 mg L−1, a sensitive sensor with long term stability was obtained. The sensor responds rapidly to the pH changes in a range of 1–10 with a response time of 3.0 min and repeatability better than 0.3% (RSD). The sensor was mounted in the quartz cells and successfully applied for pH monitoring. No evidence of leaching of the dye or any signal drift was observed.

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