Upconversion Nanoparticles Dramatically Promote Plant Growth Without Toxicity

Upconversion nanophosphors (UCNPs) have been widely used in bioscience and bioimaging, but the effect of UCNPs on plants and on animals after subsequent oral ingestion of the plants has not been studied previously. Herein, we investigate the effects of UCNPs on plant development using mung beans as a model. Incubation at a high UCNP concentration of 100 μg/mL led to growth inhibition, while a low concentration of 10 μg/mL promoted their development. Confocal imaging showed that UCNPs accumulated in the seeds and were transferred from seeds and roots to stems and leaves through the vascular system. Quantitative study by radioanalysis showed the distribution of UCNPs in the plant on the 5th day after incubation decreased in the order (root > seed > leaf > stem). After UCNP-treated bean sprouts were orally ingested by mice, UCNPs were completely excreted with feces, without absorption of residual amounts. Histology and hematology results showed no detectable toxic effects of UCNP-treated mung beans on exposed mice.