While few publications have documented the uptake of nanoparticles in plants, this is the first study describing uptake and distribution of the ultra-small anatase TiO 2 in the plant model system Arabidopsis. We modified the nanoparticle surface with Alizarin red S and sucrose, and demonstrated that nanoconjugates traversed cell walls, entered into plant cells, and accumulated in specific subcellular locations. Optical and X-ray fluorescence microscopy co-registered the nanoconjugates in cell vacuoles and nuclei. KeywordsAnatase TiO 2 nanoparticles; TiO 2 nanoconjugates; Arabidopsis thaliana; X-ray fluorescence microscopy (XFM)The application of nanotechnology to plant systems has lagged behind nanomedicine and nanopharmacology in spite of its potential to generate new tools for the delivery of fertilizers, herbicides and insecticides 1 , new ways to manipulate plant genomes 2 and new methods to capture and isolate plant natural products. Compared to the thousands of studies describing the uptake and trafficking of nanoparticles (NPs) in biological systems other than plants, less than twenty reports discussed NP uptake by plant species. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] These studies involved different plant species and different types of NPs which were delivered to intact plants, dissected plant organs or protoplasts using a wide range of application methods. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Despite the absence of systematic analyses, it has been determined that plants can take up NPs from the environment and transport them through the vascular system to various shoot organs. 4,9,15 However, little is known about the uptake mechanisms involved or the subcellular localization and distribution of the internalized NPs. 16 Uptake efficiency has also Figure S1), and show additional data describing NC distribution and localization in roots, hypotocyls and cotyledons (Figures S2, S3 and S4). This material is available free of charge via the Internet at http://pubs.acs.org. Here, we report on the uptake and localization of anatase titanium dioxide (TiO 2 ) NPs smaller than 5 nm in the plant model system Arabidopsis thaliana. We chose to study the Col-0 accession because this is the most commonly used ecotype within the Arabidopsis research community. 22 The numerous resources developed for this genetic background 23,24 will not only facilitate future analyses of the molecular mechanisms of uptake, intracellular localization and trafficking of NPs, but will also provide opportunities for NP-mediated manipulations of the Arabidopsis genome. In addition, the well-characterized Arabidopsis null mutants and overexpression lines for enzymes of various biochemical pathways offer the possibility for the targeted in planta chemical modification of NP surface with pathway intermediates. TiO 2 NPs with average diameters of 2.8 ± 1.4 nm and NP dispersity of 43% (see Supporting information) were synthesized by a low-temperature alkaline hydrolysis route as described previously 2...

Resistance to anthracyclines and other chemotherapeutics due to P-glycoprotein (PGP)-mediated export is a frequent problem in cancer treatment. Here we report that iron oxide-titanium dioxide core-shell nanocomposites can serve as efficient carriers for doxorubicin to overcome this common mechanism of drug resistance in cancer cells. Doxorubicin nanocarriers (DNCs) increased effective drug uptake in drug-resistant ovarian cells. Mechanistically, doxorubicin bound to the TiO2 surface by a labile bond that was severed upon acidification within cell endosomes. Upon its release doxorubicin traversed the intracellular milieu and entered the cell nucleus by a route that evaded PGP-mediated drug export. Confocal and x-ray fluorescence microscopy with flow cytometry were used to demonstrate the ability of DNC to modulate transferrin uptake and distribution in cells. Increased transferrin uptake occurred through clathrin-mediated endocytosis, indicating that nanocomposites and DNCs may both interfere with removal of transferrin from cells. Together, our findings show that DNCs not only provide an alternative route of delivery of doxorubicin to PGP-over-expressing cancer cells, but may also boost the uptake of transferrin-tagged therapeutic agents.