Used in optical sensors for detecting metal ions, particularly in ion-selective electrodes and thin-film sensors. It functions as a pH-sensitive dye that changes color in response to changes in proton or metal ion concentration, enabling real-time monitoring of analytes in environmental, clinical, and industrial samples. Commonly applied in polymeric membranes for continuous, reversible detection of ions like copper and mercury due to its strong optical response and selectivity. Also utilized in microfluidic devices and biosensors where visual or spectrophotometric readout is required.