Fate and Physiological Effects of Foliar Selenium Nanoparticles in Wheat

Selenium (Se) biofortification of wheat using Se nanoparticles (NPs) represents a promising intervention to address Se deficiency in the global population. However, concerns persist regarding potential health risks associated with NPs exposure, and importantly, the mechanisms of uptake, translocation and transformation of Se NPs in plants remain incompletely understood. Here, a field experiment spanning the full life cycle of wheat was conducted to evaluate the long-term effects of two sizes of Se NPs (∼60 nm and ∼210 nm), compared to conventional ionic Se on crop yield, nutritional profile, and Se biofortification, with a focus on understanding underlying mechanisms of action. Se fertilizers were applied as foliar sprays at the jointing, booting, and filling stages at doses of 5, 10, and 20 g Se/ha, respectively. Results showed that Se NPs outperform traditional ionic Se fertilizers in enhancing wheat yield (27.13%), starch content (20.94%), as well as grain Se concentration (32 times) and bioaccessibility (39.93%). The positive effects can be attributed to the advantages of NPs' size and controlled-release properties, which nutritionally supplement plants through direct uptake and subsequent gradual release of Se ions. Surprisingly, larger Se NPs exhibited better performance than smaller ones, demonstrating higher fertilizer utilization efficiency (up to 59%). Single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS) revealed that Se NPs efficiently delivered Se to the grain, where it accumulates in ionic form rather than as nanoparticles, thereby avoiding the potential risk of direct human ingestion of NPs. This work advances our understanding of the uptake, transformation, translocation, and ultimate accumulation of Se NPs as part of a wheat biofortification strategy, while also providing information on the long-term implications of Se NPs as a safe and sustainable nanobased agricultural strategy.