Coating iron oxide nanoparticles with mesoporous silica reduces their interaction and impact on S. oneidensis MR-1

Joseph T. Buchman, Thomas Pho, Rebeca S. Rodriguez, Z. Vivian Feng, Christy L Haynes

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

Here, we investigate the impact of iron oxide nanoparticles (IONPs) and mesoporous silica-coated iron oxide nanoparticles (msIONPs) on Shewanella oneidensis in an aerobic environment, which is likely the main environment where such nanoparticles will end up after use in consumer products or biomedical applications. Monitoring the viability of S. oneidensis, a model environmental organism, after exposure to the nanoparticles reveals that IONPs promote bacterial survival, while msIONPs do not impact survival. These apparent impacts are correlated with association of the nanoparticles with the bacterial membrane, as revealed by TEM and ICP-MS studies, and upregulation of membrane-associated genes. However, similar survival in bacteria was observed when exposed to equivalent concentrations of released ions from each nanomaterial, indicating that aqueous nanoparticle transformations are responsible for the observed changes in bacterial viability. Therefore, this work demonstrates that a simple mesoporous silica coating can control the dissolution of the IONP core by greatly reducing the amount of released iron ions, making msIONPs a more sustainable option to reduce perturbations to the ecosystem upon release of nanoparticles into the environment.

Original languageEnglish (US)
Article number124511
JournalChemosphere
Volume237
DOIs
StatePublished - Dec 2019

Bibliographical note

Funding Information:
This work was supported by the National Science Foundation under the Center for Sustainable Nanotechnology, CHE-1503408 . The CSN is part of the Centers for Chemical Innovation Program. J.T.B. acknowledges support by a National Science Foundation Graduate Research Fellowship (grant number 00039202 ). TEM imaging in this study was carried out in the Characterization Facility, University of Minnesota , which receives partial support from the National Science Foundation through the MRSEC program. The authors are grateful to Fang Zhou at the Characterization Facility for microtome preparation of resin-embedded samples for TEM. The authors gratefully acknowledge Elizabeth Lundstrom for ICP-MS analysis of the NP binding samples as well as the iron dissolution samples as part of the University of Minnesota Earth Sciences Department. The authors thank Dr. Erin Carlson for use of her iQ5 real-time PCR detection system.

Funding Information:
To prepare the nanoparticles for imaging by transmission electron microscopy, they were first diluted to a suspension of approximately 0.5?mg/mL (IONPs were used at ?2?mg/mL) and sonicated for 10?min to ensure dispersal. Then, for MSNs and msIONPs, a 200 mesh copper grid with Formvar and carbon supports (Ted Pella, Inc., Redding, CA) was briefly dipped into the suspension. For IONPs, a 3??L drop of the suspension was placed onto the grid surface. All grids were dried near an open 65??C oven prior to imaging with a FEI Tecnai T12 transmission electron microscope. To acquire the images, the microscope was used at an operating voltage of 120?kV. Size analysis was performed on the images using ImageJ (Schneider et al., 2012), with size determined by measuring the diameter of at least 500 randomly chosen nanoparticles (it is assumed that all nanoparticles are spherical) using built-in functions of ImageJ.The bacterial samples were prepared for TEM by adapting previously reported methods (Schrand et al., 2010; Buchman et al., 2018). The samples were washed thrice without resuspension using 0.1?M cacodylate buffer, centrifuging at 500?g for 2?min between each wash step. To fix the sample, the pellet was resuspended in 2.5% glutaraldehyde in 0.1?M cacodylate buffer for 50?min, followed by centrifuging at 800?g for 5?min. The pellet was again washed three times with 0.1?M cacodylate buffer without resuspension. To dehydrate the samples, a series of ethanol washes was done at increasing ethanol concentrations in water, using each concentration twice (30%, 50%, 70%, 80%, 95%, and 100% ethanol). The samples were then washed three times with propylene oxide prior to using a 2:1 propylene oxide:resin mix for 2?h, uncovered. This 2:1 mixture was replaced with 1:1 propylene oxide:resin to soak overnight, after which it was replaced with fresh 1:1 propylene oxide:resin for 4?h. The samples were then incubated in pure resin overnight, which was replaced with fresh resin the next day. To cure the resin, the samples were put in a 40??C oven for 24?h and a 60??C oven for 48?h. The samples were sliced into ?70?-nm-thick sections using a LEICA EM UC6 ultramicrotome, which were stained with uranyl acetate and lead citrate. The slices were placed on 200 mesh copper grids with carbon and Formvar supports (Ted Pella, Inc., Redding, CA). Images of the samples were acquired using a FEI T12 transmission electron microscope at an operating voltage of 120?kV.This work was supported by the National Science Foundation under the Center for Sustainable Nanotechnology, CHE-1503408. The CSN is part of the Centers for Chemical Innovation Program. J.T.B. acknowledges support by a National Science Foundation Graduate Research Fellowship (grant number 00039202). TEM imaging in this study was carried out in the Characterization Facility, University of Minnesota, which receives partial support from the National Science Foundation through the MRSEC program. The authors are grateful to Fang Zhou at the Characterization Facility for microtome preparation of resin-embedded samples for TEM. The authors gratefully acknowledge Elizabeth Lundstrom for ICP-MS analysis of the NP binding samples as well as the iron dissolution samples as part of the University of Minnesota Earth Sciences Department. The authors thank Dr. Erin Carlson for use of her iQ5 real-time PCR detection system.

Publisher Copyright:
© 2019 Elsevier Ltd

Keywords

  • Bacteria
  • Dissolution
  • Gene expression
  • Iron oxide
  • Nanotoxicity
  • Silica

How much support was provided by MRSEC?

  • Shared

Reporting period for MRSEC

  • Period 6

PubMed: MeSH publication types

  • Journal Article

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