Bioimaging and distribution of unmodified and polyethylene glycol-modified up-converting SrF2:Yb3+,Er3+ nanoparticles in Tenebrio molitor larvae and their impact on lifespan, moulting, and metabolism

Lanthanide-doped up-converting nanoparticles (UCNPs) are promising structures for researchers due to their unique properties and luminescence capabilities under near-infrared (NIR) excitation. They have found applications in various industries and scientific fields, including biology, medicine, and chemistry. In this study, we investigated the biodistribution and accumulation of SrF 2 :Yb 3+ ,Er 3+ UCNPs (bare UCNPs) and SrF 2 :Yb 3+ ,Er 3+ @polyethylene glycol UCNPs (PEG-modified UCNPs) in tissues and organs of Tenebrio molitor larvae and analysed their impact on larval development, lifespan and metabolic status. We successfully visualised the presence of bare and PEG-modified UCNPs in T . molitor larvae and determined their distribution across different organs and tissues. An elemental analysis revealed no differences in the levels of either UCNP type in whole-body invertebrate samples. However, the imaging method revealed that PEG-modified UCNPs penetrate mealworms more effectively than bare UCNPs do at lower concentrations. These outcomes suggest that the distribution of PEG-modified UCNPs is greater than that of bare UCNPs in insects. Toxicity assays revealed that neither of the tested UCNPs had adverse effects on the lifespan or development of T. molitor at the tested concentrations. However, some of the experimental treatments altered lipid and carbohydrate levels. Specifically, bare UCNPs led to increased glycerol levels in the haemolymph after 3 h of incubation (at 100 µg/mL) and decreased triglyceride (TAG) levels in the fat body 24 h after injection (at 500 µg/mL). PEG-modified UCNPs increased glycogen levels in the fat body after 3 h of incubation (at 100 µg/mL). There were no changes in the other parameters. Overall, our findings revealed the accumulation of UCNPs in specific tissues and highlighted the influence of PEG modification on these processes. The studied UCNPs exhibited low toxicity and demonstrated the potential for effective bioimaging within insect organisms (especially those with PEG surface modifications). Moreover, the results showed that investigating the effects on metabolism is important, even if the impacts on lifespan and development are not observed. • SrF₂:Yb³⁺,Er³⁺ and PEG-UCNPs were used for imaging in invertebrate tissues. • PEG-UCNPs were detectable at lower doses than bare UCNPs. • Neither UCNP type affected larval growth or development. • UCNPs only slightly altered glycerol, TAG, or glycogen. • UCNPs showed bioimaging potential with low toxicity.