Tailoring colour changes of optical sensor materials by combining indicator and inert dyes and their use in sensor layers, textiles and non-wovens

The appropriate combination of absorbance-based indicator dyes and inert dyes allows colour changes from green to red to be observed. In detail, a pH indicator with a yellow to red colour change upon exposure to alkaline buffers is combined with a blue and pH-insensitive dye. The resulting colour change of indicator plus inert dye is more easily visible than the original colour change and is more easily interpreted in terms of a “traffic light” change. The approach can be used in optical sensor layers but preferably on textile materials to provide fast and understandable information on e.g. wound pH or pH of detergent solutions. Accordingly, a facecloth can detect pH of washing agents and thus inform about a possible irritation of the skin of babies or patients suffering from dermatitis while sensor swabs may give an indication on pH in wounds and thus on the healing progress. Since all dyes are covalently linked to the polymer layers and textiles by using the vinylsulfonyl bonding to cellulose, no leaching can occur and contamination of samples is avoided.