Upconverting vs. fluorescent labels for visualizing distribution and uptake of nanoplastics: a Daphnia magna case study

Abstract

Micro- and nanoplastics (MNPLs) are pervasive environmental contaminants, raising concerns for ecosystems and human health. Nanoplastics (NPLs), in particular, present unique analytical challenges due to their minute size, which makes their detection and study in complex biological systems difficult. Consequently, toxicological studies frequently use commercially available fluorescent polystyrene (PS) particles as model NPLs. These models, however, mainly have two drawbacks: limited environmental relevance and inadequate visualization in biological tissues, largely due to overlapping tissue autofluorescence. In this study, we address these issues by preparing surfactant-free model NPLs (UC-PS) labeled with Yb3+,Er3+-doped upconverting nanoparticles (UCNPs) that convert near-infrared excitation to visible emission. UC-PS were compared with a commercial NPL labeled with a fluorescent dye (fluo-PS). Both types consisted of spherical particles of ~100 nm in diameter, but exhibited distinct luminescent properties, as shown by spectroscopy and fluorescence microscopy. UC-PS and fluo-PS at concentrations of 0-100 µg/mL did not affect Daphnia magna’s growth rate after 72-h exposure. Importantly, unlike fluo-PS, UC-PS was clearly visualized within Daphnia magna’s intestine despite strong tissue autofluorescence. This work demonstrates the advantages of UCNP-labeled NPL models over conventional fluorescent NPLs and recommends their use for accurate visualization of MNPLs uptake in aquatic organisms.