1. Antibacterial and antitumoral activity
of ceria nanoparticles obtained by an eco-friendly sol-gel method
A. Mesaros1, L. Mirea-Popa2, L. Perju-Dumbrava2, O. Pop3, Z. Diaconeasa3, E. Ware4, F. Goga5, C. Socaciu3
1Technical University of Cluj-Napoca, Superconductivity, Spitronic and Surface Science Center – C4S, Cluj-Napoca, Romania
2University of Medicine and Pharmacy, Department of Clinical Neurosciences, Cluj-Napoca, Romania
3Faculty of Food Science and Technology, University of Agricultural Science and Veterinary Medicine Cluj-Napoca, Cluj-Napoca, Romania
4Imperial College London, Exhibition Road, South Kensington, London SW72AZ, United Kingdom
5Babes-Bolyai University, Faculty of Chemistry and Chemical Engineering, 11 Arany Janos Street, Cluj-Napoca, Romania
Abstract: Ceria nanoparticles have been successfully synthesized using a new facile and eco-friendly sol-gel method. This approach is based on the thermal decomposition of ceric ammonium nitrate, Ce(NH4)2(NO3)6 in the presence of a sucrose,-pectin mixture. The chemical nature, structure and morphology of the CeO2 nanoparticles (nps) have been investigated by FT-IR, XRD, XPS, EPR and TEM. The XRD investigations reveal the formation of the fluorite crystal structure, while the TEM images show the formation of spherical nanoparticles with an average particle size range between 5 to 10 nm. Nanoceria switches between Ce4+ and Ce3+ states creating oxygen vacancies and this capability is similar to that of biological antioxidants. Thus, the antioxidant properties of CeO2 nps have been studied by using the EPR spectroscopy coupled with the spin trapping probe technique. As spin trapping agent was used 5,5-dimethyl-1-pyrroline N-oxide (DMPO, Sigma-Aldrich) dispersed in DMSO solution. The CeO2 nps antibacterial effect against four pathogenic bacteria: Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, Bacillus cereus has been studied. The cytotoxic effect induced by the ceria nanoparticles has been evaluated on two cell lines, D407 (human retinal pigment epithelial) and B16-F10 (melanoma murine), as well. The results make the as-obtained ceria nanoparticles promising candidates for biomedical applications.
Synthesis: For the CeO2 nps synthesis, a new facile and eco-friendly sol-gel method was followed. A ceric ammonium nitrate, Ce(NH4)2(NO3)6, solution (0.05 M) and a sucrose, C12H22O11, solution (0.1 M) have been prepared using as solvent milli-Q water, at 65 oC, under magnetic stirring. The two solutions have been mixed in the presence of the pectin (the sucrose to pectin weight ratio was 1:5). The pH value has been monitored during the synthesis and no correction was necessary to maintained an acidic medium in the solution. The as-obtained mixture has been dried in air, on the sand bath. At 215 oC a spontaneous combustion of the synthesis mixture has been observed and a dispersed yellow powder has been obtained. The following chemical reaction can be considered in the formation of ceria nanoparticles:
Ce3+ + 2NH4+ + 6NO3- + 2(C12H22O11) + 26O2 → CeO2 + 24CO2 + 26H2O + 8NO2
FT-IR spectroscopy
XRD
CeO2
fluorite type
crystalline structure
a = Å
Ce2O3
hexagonal crystalline
structure
a = Å, c = Å
Ce3+
Ce2O3 + 2[OH∙]  2CeO2 + H2O
Ce2O3 + O2 + 2H+ ← 2CeO2 + H2O
Oxidation – reduction
cycle
Regenerative
Nano-Ceria
Ce4+
XPS spectroscopy
EPR spectroscopy
TEM-HRTEM-SAED
Antibacterial activity
Antitumoral activity
Bacterial strains
CeO2 nps MIC (mg/ml)
CeO2 nps MBC (mg/ml)
Escherichia coli
1.00 ± 0.02
2.5 ± 0.01
Salmonella typhimurium
1.55± 0.01
3.5 ± 0.03
Staphylococcus aureus
2.20± 0.04
4.2 ± 0.04
3.0 ± 0.02
Bacillus cereus
1.65± 0.03
 Bacterial strains
CeO2 NP concentration (mg/ml)
Gentamicin
(mg/ml)
0.5
1.5
2.5 1
Zone of inhibition (mm diameter)
Escherichia coli
2.4
4.1 5
Salmonella typhimurium GR
3.2
4.5
Staphylococcus aureus -
2.2 2
Bacillus cereus
3.5
Conclusions
Ceria nps nanoparticles have been successfully synthesized using a new facile and eco-friendly sol-gel method. The XRD and TEM-SAED studies reveal the formation of CeO2 fluorite type crystalline structure. The morphology (shape and size) were investigated by TEM and HRTEM. The CeO2 crystallites present spherical shape are agglomerated and a size distribution in the 5-8 nm range. The presence of a small amount of the organic residues are observing in the FTIR spectra of ceria nps. The EPR measurements, using DMPO as spin trapping agent, are revealing the generation of reactive oxygen species (ROS), namely hydroxyl radical and singlet oxygen. The existence of Ce+3 and Ce+4 ions is evidence by XPS measurements. Ceria nps are demonstrated high growth inhibition for the sample where E. coli was the targeted pathogen, and good inhibition for the rest of the tested pathogens. It can be concluded that the growth inhibition results can vary depending on the type of the pathogenic bacteria and the concentration of the ceria nps. Regarding the antitumoral activity the treatment for 24h with ceria nps decrease all cells viability exposed to the treatment in a dose-dependent manner. Ceria nps treatment on D407 cells showed viability of 79% for 24 h incubation while for B16-F10 and A549 cell lines the viability was 61.57% and 65.84% respectively. This proves the ability of CeO2 nps to inhibit cancer cells proliferation in a higher manner comparing to normal cells. The results clearly demonstrate the great potential of the as-obtained ceria nps in the biomedical domain.
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Acknowledgments: This research was supported by UEFISCDI Project No. PN-II-RU-TE , Contract No 16/