Optimization of ZnGa₂O₄:Cr³⁺ Nanoparticle Synthesis Exhibiting Persistent Luminescence for Nanoplastic Labelling and Imaging in Daphnia magna

Abstract

Nano- and microplastic pollution is one of modern science’s most pressing environmental challenges. Its presence has been reported in soil, water, air, aquatic species, and humans. Despite its widespread occurrence, tracking plastic particles within organisms remains challenging. Therefore, developing new visualization methods is crucial for understanding how nano- and microplastics are distributed and absorbed in biological systems. A promising solution lies in nanoparticles (NPs) capable of persistent luminescence, such as ZnGa2O4:Cr3+, which, as labels, enable background-free detection in the first biological window range. In this work, three different synthesis methods of the ZnGa2O4:Cr3+ NPs, i.e., precipitation, hydrothermal, and solvothermal are compared, and their optimization for the best spectroscopic properties. The optimized NPs are then applied for polystyrene microparticles labeling and successfully used to track microplastic uptake and distribution in Daphnia magna as a model aquatic organism.