Effects of Polydopamine Microspheres Loaded with Silver Nanoparticles on Lolium multiflorum: Bigger Size, Less Toxic

The rapid development of nanotechnology and its widespread use have given rise to serious concerns over the potential adverse impacts of nanomaterials on the Earth's ecosystems. Among all the nanomaterials, silver nanoparticles (AgNPs) are one of the most extensively used nanomaterials due to their excellent antibacterial property. However, the toxic mechanism of AgNPs in nature is still unclear. One of the questions under debate is whether the toxicity is associated with the size of AgNPs or the silver ions released from AgNPs. In our previous study, a sub-micron hybrid sphere system with polydopamine-stabilized AgNPs (Ag@PDS) was synthesized through a facile and green method, exhibiting superior antibacterial properties. The current study aims to explore the unique toxicity profile of this hybrid sphere system by studying its effect on germination and early growth of Lolium multiflorum, with AgNO₃ and 15 nm AgNPs as a comparison. The results showed the seed germination was insensitive/less sensitive to all three reagents; however, vegetative growth was more sensitive. Specifically, when the Ag concentration was lower than 40 mg/L, Ag@PDS almost had no adverse effects on the root and shoot growth of Lolium multiflorum seeds. By contrast, when treated with AgNO₃ at a lower Ag concentration of 5 mg/L, the plant growth was inhibited significantly, and was reduced more in the case of AgNP treatment at the same Ag concentration. As the exposures of Ag@PDS, AgNO₃, and AgNPs increased, so did the Ag content in the root and shoot. In general, Ag@PDS was proven to be a potential useful hybrid material that retains antibacterial property with light phytotoxicity.