In the present paper, however, we introduce the combination of one absorbance-based pH indicator dye with another
absorbance-based, albeit analyte-inert dye in order to provide colour changes that are more visible for the human eye. Furthermore, we achieve colour changes with well-known meaning, e.g. “traffic-light” changes from green to red and we guarantee stable response by covalently immobilising the dyes to the polymer matrix.