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. 2007 May 24;90(213902):2139021-2139023.
doi: 10.1063/1.2742324.

Selective toxicity of zinc oxide nanoparticles to prokaryotic and eukaryotic systems

K M Reddy  1 , Kevin Feris, Jason Bell, Denise G Wingett, Cory Hanley, Alex Punnoose
Affiliations

Selective toxicity of zinc oxide nanoparticles to prokaryotic and eukaryotic systems

K M Reddy et al. Appl Phys Lett. .

Abstract

We report on the toxicity of ZnO nanoparticles (NPs) to gram-negative and gram-positive bacterial systems, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), and primary human immune cells. ZnO NP (~13 nm) showed complete inhibition of E. coli growth at concentrations 3.4 mM, whereas growth of S. aureus was completely inhibited for 1 mM. Parallel experiments using flow cytometry based assays clearly demonstrated that growth inhibitory properties of ZnO NP were accompanied by a corresponding loss of cell viability. Identical ZnO NP had minimal effects on primary human T cell viability at concentrations toxic to both gram-negative and gram-positive bacteria. Collectively, these experiments demonstrate selectivity in the toxic nature of ZnO NP to different bacterial systems and human T lymphocytes. Developing selective toxicity to biological systems and controlling it by NP design could lead to biomedical and antibacterial applications.

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Figures

FIG. 1
FIG. 1
(a) Optical absorption spectrum of ZnO NP. The inset shows the XRD pattern of the sample and (b) TEM image of the ZnO NPs. The inset shows a selected area electron diffraction pattern confirming the crystalline ZnO phase and (c) plot showing particle size distribution.
FIG. 2
FIG. 2
(Color online) (a) Means and standard errors of CFU per milliliter of E. coli and S. aureus incubated for 24 h in LB media in the presence of different concentrations of ZnO NP; n=3. X and * indicate measured ZnO NP concentrations at which no CFU counts of E. coli and S. aureus, respectively, were observed; (b) viability of primary human CD4+ T cells isolated from peripheral blood samples treated with various concentrations of ZnO NP or bulk ZnO for 20 hrs; n=3.
FIG. 3
FIG. 3
(Color online) Effect of ZnO NP exposure time on the viability and growth of E. coli and S. aureus. Plots present mean CFU per milliliter (± standard error, n=3) of E. Coli (a) and S. aureus (b) exposed to different concentrations of ZnO NP for 0, 6, 12, 24, and 48 h. X and * indicate measured ZnO concentrations at which no CFU counts of E. coli and S. aureus, respectively, were observed.
FIG. 4
FIG. 4
Relative bacterial viability determined by flow cytometry. Samples of bacteria were prepared, stained, and analyzed as outlined in the text and viability determined by a two-parameter comparison of green and red fluorescence emissions. Bacteria were gated by forward scatter and side scattering light properties and NPs excluded from analysis based on the absence of fluorescence. R3 depicts the region containing dead cells and R4 depicts the region containing live cells. (a) E. coli treated with 5 mM ZnO NPs for 15 h. (b) S. aureus treated with 2 mM ZnO NPs for 15 h.
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