Construction of a ratiometric phosphorescent assay with long-lived carbon quantum dots and inorganic nanoparticles for its application in environmental and biological systems

A nanohybrid-based ratiometric phosphorescent assay composed of water-soluble carbon dots (CDs) and water-dispersible lanthanide-doped inorganic nanoparticles CaTiO3:Pr3+@SiO2 is constructed. The as-prepared CDs and CaTiO3:Pr3+@SiO2 nanoparticles were systematically characterized by transmission electron microscopy (TEM), scanning electron microscopy, dynamic light scattering, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). Under a single excitation wavelength at 345 nm, a dual-emission of CDs at 446 nm and CaTiO3:Pr3+@SiO2 nanoparticles at 615 nm are detected, and the long luminescent lifetimes of the two phosphorescent emissions were confirmed by 3-D time-resolved phosphorescence emission spectra. The excellent phosphorescence performance of CDs and CaTiO3:Pr3+@SiO2 nanoparticles is utilized for the development of a ratiometric phosphorescent platform. In the presence of Hg2+, the phosphorescent emission of CDs was dramatically quenched, and that of CaTiO3:Pr3+@SiO2 nanoparticles nearly unchanged. Taking advantage of this, an effective ratiometric phosphorescent sensor unaffected by sensor concentration, background fluorescence and environmental conditions is constructed. Furthermore, the successful application of the nanohybrid phosphorescent system in water and biological samples lays the foundation for building a reliable approach to monitor heavy metal ions in complex environmental and biological samples.