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

Silica nanoparticles (SiO 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 SiO NPs of different sizes without and with a gold nanoparticle core (Au@SiO NPs) was examined. Potential interference from SiO 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 SiO NPs in roots and shoots and a decrease in the accumulation of SiO NPs in shoots with increasing particle size. However, when accumulation was monitored using Au@SiO NPs, SiO NP accumulation was significantly higher when measured by direct Si determination than by Au determination, indicating that the former overestimates the accumulation of SiO NPs. Consequently, unlike direct Si determination, tracking the gold nanoparticle core revealed an increase in SiO NP accumulation in shoots with increasing particle size. Overall, accurate determination of SiO NP bioaccumulation is imperative for appropriate bioapplications and reliable biosafety assessments of these particles.