In vivo tracking of copper-64 radiolabeled nanoparticles in Lactuca sativa

Authors: DAVIS, RYAN - University Of California; RIPPNER, DEVIN - University Of California; HAUSNER, SVEN - University Of California; PARIKH, SANJAI - University Of California; McElrone, Andrew; SUTCLIFFE, JULIE - University Of California

Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2017
Publication Date: 11/7/2017
Citation: Davis, R., Rippner, D., Hausner, S., Parikh, S., McElrone, A.J., Sutcliffe, J. 2017. In vivo tracking of copper-64 radiolabeled nanoparticles in Lactuca sativa. Environmental Science and Technology. 51(21):12537-12546. https://doi.org/10.1021/acs.est.7b03333.
DOI: https://doi.org/10.1021/acs.est.7b03333

Interpretive Summary: The [64Cu]-NP-uptake and accumulation amounts observed within lettuce seedlings were reasonable and comparable to others reports in the literature, reaching the same general conclusions that NP transport and accumulation in plants is species and size dependent.(1, 12, 16, 18, 21, 23, 30) Smaller NPs have been demonstrated to have higher accumulation in plants than larger NPs. For example, Ni-NPs (1, 3, and 9 nm) had very high NP uptake ranging from ~13'200–38'983 µg/g in mesquite.(45) The amount found in the leaves varied from 400 to 803 µg/g of mesquite with most the NPs remaining in the roots ranging from 12'835 to 38'183 µg/g.(45) Another study using small CeO2-NPs (7 nm) exhibited NP accumulation ranging from 300 to 6000 µg/g of plant (corn, soy bean, cucumber, tomato, and alfalfa) and indicated that NP accumulation was plant species dependent.(10) NP sizes above active transport ranging from 14 to 40 nm had a large variation in uptake ranging from 0.25 to 3750 µg/g of plant, but typically had accumulation ranging from ~1–1100 µg/g of plant again with the majority of the NPs contained within the root and with 0.5–183 µg/g in the leaves.(1, 15, 16, 20, 27, 29) NPs (50 nm), had accumulation in mung bean of 8 µg/g and in wheat of 32 µg/g.(32) When comparing the accumulation of two similarly sized TiO2-NPs of different crystalline structure [22 nm (rutile) and 25 nm (anatase)] in wheat different accumulation amounts were observed, suggesting size was not the only limiting factor for transportation into a plant.

Technical Abstract: Engineered nanoparticles (NPs) are increasingly used in commercial products including automotive lubricants, clothing, deodorants, sunscreens, and cosmetics and can potentially accumulate in our food supply. Given their size it is difficult to detect and visualize the presence of NPs in crop plants. Thus, new analytical tools are needed to fill this void for detection and visualization of NPs in complex biological and environmental matrices. We aimed to determine whether radiolabeled NPs could be used as a noninvasive, highly sensitive analytical tool to quantitatively track and visualize NP transport and accumulation in vivo in Lactuca sativa (lettuce) and to investigate the effect of NP size on transport and distribution overtime using a combination of autoradiography, positron emission tomography (PET)/computed tomography (CT), scanning electron microscopy (SEM), and transition electron microscopy (TEM). Azide functionalized NPs were radiolabeled via a “click” reaction with copper-64 (64Cu) chelated 1,4,7-triazacyclononane triacetic acid (NOTA) azadibenzocyclooctyne (ADIBO) conjugate ([64Cu]-ADIBO-NOTA) via copper-free Huisgen-1,3-dipolar cycloaddition reaction. This yielded radiolabeled 64Cu-NPs of uniform shape and size with a high radiochemcial purity (>99%), specific activity of 83MBq/mg of NP, and high stability (i.e., no detectable dissolution) over 24h and across a pH range of 5-9. Both PET/CT and autoradiography showed that [64Cu]-NPs entered the lettuce seedling roots and were rapidly transported to the cotyledons with the majority of the accumulation inside the roots. Uptake and transport of intact NPs was size dependent, and in combination with the accumulation within the roots suggests a filtering effect of the plant cell walls at various points along the water transport pathway. The locations of NPs within seedlings were also confirmed by SEM and TEM.