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.