combinations of different absorbance- or fluorescence-based
dyes in one optical sensor are quite common. In the case of the
absorbance-based sensors, indicator dyes are mostly combined to
extend the sensitive range of the optical sensor. One example is
to use several pH indicators of different pKa
values in one layer.Thus, the well-known limitation of optical pH sensors to 3–4 pH
units of measurement range, which makes them inferior to the
pH electrode, can be overcome.