Optical monitoring of sweat pH by a textile fabric wearable sensor based on covalently bonded litmus-3-glycidoxypropyltrimethoxysilane coating

A wearable, flexible and non-toxic pH sensor was fabricated by assembling a cotton fabric treated with an organically modified silicate (ORMOSIL) together with a miniaturized and low-power electronics with wireless interface. The pH sensible ORMOSIL was obtained via sol–gel by using litmus, a non-toxic pH indicator, and 3-glycidoxypropyltrimethoxysilane (GPTMS) as siloxane precursor. The chemical structure of the ORMOSIL was analyzed by FTIR and UV–vis spectroscopy. The electronics has been first character- ized in a standalone fashion, and successively it has been coupled to the smart fabric, in the laboratory and in preliminary on-body trials. A sweat real-time monitoring is particularly attractive for healthcare, fitness and wellness areas.