Ratiometric fluorescence sensors for the detection of HPO42- and H2PO4- using different responses of the morin-hydrotalcite complex

Two phosphate-sensing membranes were fabricated based on the selective response of the fluorescent dye, morin (MR), to phosphate ions (H2PO4- and HPO42-) by the fluorescence quenching effect. The MR adsorbed to hydrotalcite (HT) (MR-HT complex) was immobilized into two kinds of supporting materials. The fluorescence emission spectra of CdSe/ZnS quantum dots (QDs) and Pt(II) meso-tetra(pentafluorophenyl) porphine (PtP) adsorbed on polystyrene (PS) particles (PtP-PS particles) were also used as reference spectra to create ratiometric fluorescence phosphate sensors. The phosphate-sensing membrane immobilized with the MR-HT complex and PtP-PS particles in the matrix of polyurethane hydrogel and sol-gel produced a sensor that was highly sensitive to H2PO4- in the linear range of 0.1-10 mM. Hydrogen phosphate (HPO42-) was detected by the phosphatesensing membrane immobilized with the MR-HT complex and QDs in the polymer Nafion; its linear detection range was 0.01-0.2 mM HPO42-. These two phosphate-sensing membranes showed short response time, high reproducibility, less interference, and long-term stability. They were both applied for the determination of phosphate ions in artificial wastewater containing different ions. The results obtained were in good agreement with the concentrations of phosphate ions added to the artificial wastewater samples.