Synthesis and design of terbium-activated CaWO4 nanocrystals for fluorescence sensing of alkaline phosphatase and bioimaging applications

Calcium tungstate nanocrystals CaWO4 NCs represent an important family of inorganic oxides and are well-known for their rare-earth (RE) sensitizing properties. Although RE-doped CaWO4 NCs have been extensively used in the optical field, their applications as a fluorescent probe is yet to be explored. In this report, inspired by their excellent luminescence properties, we demonstrate the potential of terbium-activated CaWO4 NCs as a fluorescent probe for sensing and biological imaging applications. In our study, we successfully synthesized nano-sized water dispersible PEG coated Tb–CaWO4 NCs via a facile one-step hydrothermal route. Next, the potential of PEG–Tb–CaWO4 NCs as a fluorescent sensing probe was evaluated by employing a “signal-off–on” sensing strategy for the detection of a key disease biomarker (alkaline phosphatase, ALP). The proposed detection system realized sensitive detection of ALP with a low limit of detection of 0.5 U L−1. Moreover, the cell imaging potential of PEG–Tb–CaWO4 NCs was investigated using HeLa cells. PEG–Tb–CaWO4 NCs were internalized by HeLa cells through endocytosis and showed characteristic bright green emission, demonstrating the cell imaging potential of the as-synthesized NCs. Also, the viability study confirmed the very low cell cytotoxicity of PEG–Tb–CaWO4 NCs to HeLa cells. Overall, we highlighted the potential of PEG–Tb–CaWO4 NCs as a promising fluorescence probe for sensing and biological imaging applications.