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PdO doping tunes band-gap energy levels as well as oxidative stress responses to a Co3O4p -type semiconductor in cells and the lung

  • Author(s): Zhang, H
  • Pokhrel, S
  • Ji, Z
  • Meng, H
  • Wang, X
  • Lin, S
  • Chang, CH
  • Li, L
  • Li, R
  • Sun, B
  • Wang, M
  • Liao, YP
  • Liu, R
  • Xia, T
  • Mädler, L
  • Nel, AE
  • et al.

Published Web Location

https://doi.org/10.1021/ja501699e
Abstract

We demonstrate through PdO doping that creation of heterojunctions on Co3O4nanoparticles can quantitatively adjust band-gap and Fermi energy levels to study the impact of metal oxide nanoparticle semiconductor properties on cellular redox homeostasis and hazard potential. Flame spray pyrolysis (FSP) was used to synthesize a nanoparticle library in which the gradual increase in the PdO content (0-8.9%) allowed electron transfer from Co3O4to PdO to align Fermi energy levels across the heterojunctions. This alignment was accompanied by free hole accumulation at the Co3O4interface and production of hydroxyl radicals. Interestingly, there was no concomitant superoxide generation, which could reflect the hole dominance of a p-type semiconductor. Although the electron flux across the heterojunctions induced upward band bending, the Eclevels of the doped particles showed energy overlap with the biological redox potential (BRP). This allows electron capture from the redox couples that maintain the BRP from -4.12 to -4.84 eV, causing disruption of cellular redox homeostasis and induction of oxidative stress. PdO/Co3O4nanoparticles showed significant increases in cytotoxicity at 25, 50, 100, and 200 μg/mL, which was enhanced incrementally by PdO doping in BEAS-2B and RAW 264.7 cells. Oxidative stress presented as a tiered cellular response involving superoxide generation, glutathione depletion, cytokine production, and cytotoxicity in epithelial and macrophage cell lines. A progressive series of acute pro-inflammatory effects could also be seen in the lungs of animals exposed to incremental PdO-doped particles. All considered, generation of a combinatorial PdO/Co3O4nanoparticle library with incremental heterojunction density allowed us to demonstrate the integrated role of Ev, Ec, and Eflevels in the generation of oxidant injury and inflammation by the p-type semiconductor, Co3O4. © 2014 American Chemical Society.

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