Two-Photon Microscopy and Spectroscopy Studies to Determine the Mechanism of Copper Oxide Nanoparticle Uptake by Sweetpotato Roots during Postharvest Treatment N. J. Bonilla-Bird, † A. Paez, ∥ A. Reyes, ∥ J. A. Hernandez-Viezcas, ‡,§ C. Li, ∥ J. R. Peralta-Videa, †,‡,§ and J. L. Gardea-Torresdey* ,†,‡,§ † Environmental Science and Engineering PhD Program, The University of Texas at El Paso; 500 West University Avenue El Paso, Texas 79968, United States ‡ Department of Chemistry and Biochemistry, The University of Texas at El Paso; 500 West University Avenue, El Paso, Texas 79968, United States § UC Center for Environmental Implications of Nanotechnology (UC CEIN), The University of Texas at El Paso, 500 West University Avenue, El Paso, Texas 79968, United States ∥ Department of Physics, The University of Texas at El Paso, 500 West University Avenue, El Paso, Texas 79968, United States * S Supporting Information ABSTRACT: The interaction of engineered nanoparticles with plant tissues is still not well understood. There is a lack of information about the effects of curing (postharvest treat- ment) and lignin content on copper uptake by sweetpotato roots exposed to copper-based nanopesticides. In this study, Beauregard-14 (lower lignin) and Covington (higher lignin) varieties were exposed to CuO nanoparticles (nCuO), bulk CuO (bCuO), and CuCl 2 at 0, 25, 75, and 125 mg/L. Cured and uncured roots were submerged into copper suspensions/ solutions for 30 min. Subsequently, root segments were sliced for imaging with a 2-photon microscope, while other root portions were severed into periderm, cortex, perimedulla, and medulla. They were individually digested and analyzed for Cu content by inductively coupled plasma-optical emission spectroscopy. Microscopy images showed higher fluorescence in periderm and cortex of roots exposed to nCuO, compared with bCuO. At 25 mg/L, only bCuO showed higher Cu concentration in the periderm and cortex of Beauregard-14 (2049 mg/kg and 76 mg/kg before curing; 6769 mg/kg and 354 mg/kg after curing, respectively) and in cortex of Covington (692 mg/kg before curing and 110 mg/kg after curing) compared with controls (p ≤ 0.05). In medulla, the most internal tissue, only Beauregard-14 exposed to 125 mg bCuO/L showed significantly (p ≤ 0.05) more Cu before curing (17 mg/kg) and after curing (28 mg/kg), compared with control. This research has shown that the 2-photon microscope can be used to determine CuO particles in nondyed plant tissues. The lack of Cu increase in perimedulla and medulla, even in roots exposed to high CuO concentrations (125 mg/L), suggests that nCuO may represent a good alternative to protect and increase the shelf life of sweetpotato roots, without exposing consumers to excess Cu. ■ INTRODUCTION The literature indicates a rapid increase in the use of nanomaterials (NMs) in agriculture industry. Currently, 9% of the nanoproducts targeted for agri/feed/food application are used in agriculture. 1 Moreover, there are several NMs in development for application as nanopesticides or nano- fertilizers. Nanocompounds of zinc, iron, and copper have been shown to have great potential as nanofertilizers. 2 In addition, copper-based NMs, whose global production for 2010 was estimated at 200 tons, 3 may have additional applications, since Cu has been approved as a pesticide in organic agriculture. 4 The fast development of agriculture- oriented nanoproducts would reduce the amount of Cu used in the production and shelf preservation of several types of produce. So far, several Cu-based nanoparticles (NPs) have been tested to control fungus and bacteria, with promising results. CuO NPs, (nCuO), have proven to be efficacious for controlling coliform bacteria in ultrafiltrated cheese. 5 It was also reported that Cu-based NPs are able to control fungi at Received: May 24, 2018 Revised: July 27, 2018 Accepted: July 31, 2018 Published: July 31, 2018 Article pubs.acs.org/est Cite This: Environ. Sci. Technol. XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acs.est.8b02794 Environ. Sci. Technol. XXXX, XXX, XXX−XXX Downloaded via UNIV OF TEXAS AT EL PASO on August 24, 2018 at 19:36:04 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.