In-vivo imaging of the uptake of upconversion nanoparticles by plant roots

Watering of Phalaenopsis and Arabidopsis plants with an aqueous colloidal solution of NaYF4:Yb,Er nanoparticles leads to uptake and transport of nanoparticles into the plants within a few days. Characteristic upconversion emission of the particles can be excited in the shoot and the leaves of the plants. Uptake of particles by the root was studied by confocal laser-scanning microscopy using excitation in the near-infrared. We demonstrated that nanoparticles are able to enter the stele of the plant root and thus the long distance transport system despite their relatively large size in comparison to the size of the structures responsible for the transport.