Foliar application of engineered nanomaterials to crops is an emerging strategy for enhancing crop yield while reducing fertilizer use. However, the pathway and functionalization of nanoparticles in planta following foliar application have not been well characterized. Here, we have developed a Mesoporous silica-based nanocarrier to deliver Zn (as ZnO nanoparticles) to plants (~70nm). Different techniques were used to verify that the designed ZnO@MSN could be taken up and translocated in tomato plants following foliar application. Synchrotron-based nanoholotomography revealed that the MSN particles could translocate via an apoplastic pathway from the plant epidermis to the plant vascular. Mass spectrometry imaging techniques and synchrotron-based X-ray fluorescence techniques further suggest that the MSNs are translocated via the phloem from the treated leaf to other parts of the plant. Interestingly, the chemical state of Si also transformed along the translocation pathway. X-ray fluorescence and micro-X-ray fluorescence revealed that the Si from silica has transformed into a more soluble silicate species and an organosilicon species featuring a Si-C bonding environment. The advanced techniques provided cross-validation that more significant nanomaterials, with a diameter up to 70nm, could be taken up and translocated in planta, far larger than the previous consensus that only particles within 20nm can cross plant cell walls. These results provided valuable insight into how NPs behave in plants and guided the future direction of NPs designing for agriculture.
