Nonselective uptake of silver and gold nanoparticles by wheat

Metallic nanoparticles (NPs) show unique reactivity to crop plants, but the uptake mechanisms remain unclear. We quantitatively evaluated the phytoavailability of particles to wheat (Triticum aestivum L.) in hydroponics upon exposure to AgNPs (15 nm) or AuNPs (13 and 33 nm). Particles were physically separated from the released Ag ions by a dialysis membrane, under which particle-specific uptake of AgNPs could be discerned. Plants did not differentiate AgNPs and AuNPs during particle uptake, with uptake rate constants of 1.1 ± 0.1, 1.2 ± 0.3, and 1.2 ± 0.1 L kg^-1 h^-1 for AgNPs, AuNPs (13 nm), and AuNPs (33 nm), respectively. We found little effect of particle size (13 or 33 nm AuNPs) or core composition (Ag or Au) on particle bioavailability. Plants stimulated the subsequent uptake of Evans blue stain and showed cell damage in root tips. These results imply similar physiological processes involved in particle-specific uptake of AgNPs and AuNPs. The internalization of particles was further confirmed by single particle inductively coupled plasma mass spectrometry (spICP-MS) and transmission electron microscope-energy dispersive spectrometer (TEM-EDS) analysis. The work here builds the knowledge base for the nature of particle-specific uptake of different NP types by crop plants.