Reversible and universal pH sensing cellulose nanofibers for health monitor

•A universal pH sensor based on cellulose nanofiber and a natural pigment is developed.•pH sensor is sensitive at all pHs and exhibits reversible halochromic transition.•This universal pH sensor is a potential material to be used as a health monitor. Development of an eco-friendly, reversible, and universal pH sensor based on electrospun cellulose nanofiber functionalized with a natural pigment is described in this study. A natural pigment from red cabbage has been extracted and incorporated onto the electrospun non-woven cellulose fibers by means of adsorption and chemical cross-linking techniques. The results revealed that the developed biocomposite is a universal pH sensor which is capable of detecting pH values in the range of 1–14 by indicating the unique color code against each pH. It was also found that the pH sensing was stable at different temperatures and at prolonged time. Moreover, the colors were reversible and the pH sensor was recyclable. Present study opens up new possibilities for using the developed universal pH sensor as a health monitor.