Direct determination of silicon overestimates the accumulation and translocation of SiO₂ nanoparticles in rice seedlings

Silica nanoparticles (SiO₂ NPs) have numerous applications in agriculture, but may also pose significant risks to plants. Nevertheless, their bioaccumulation, an important determinant of their risks, was often not accurately measured due to the lack of reliable methods. In this study, the accumulation in rice seedlings of SiO₂ NPs of different sizes without and with a gold nanoparticle core (Au@SiO₂ NPs) was examined. Potential interference from SiO₂ NP dissolution was minimized by lowering the pH of the uptake medium, which did not result in any observable adverse bioeffects. Under this condition, the direct determination of Si showed the significant accumulation of SiO₂ NPs in roots and shoots and a decrease in the accumulation of SiO₂ NPs in shoots with increasing particle size. However, when accumulation was monitored using Au@SiO₂ NPs, SiO₂ NP accumulation was significantly higher when measured by direct Si determination than by Au determination, indicating that the former overestimates the accumulation of SiO₂ NPs. Consequently, unlike direct Si determination, tracking the gold nanoparticle core revealed an increase in SiO₂ NP accumulation in shoots with increasing particle size. Overall, accurate determination of SiO₂ NP bioaccumulation is imperative for appropriate bioapplications and reliable biosafety assessments of these particles.