ZnO nanoparticles were produced through green synthesis using essential oils (lavender or thyme oils) mediated by Pluronic-assisted co-precipitation, followed by calcination at 500 °C. One part of the particles was doped with Pr₂O₃ (0.3-1 at.% ).

PXRD analysis, FTIR spectroscopy, SEM, EDS, and XPS were performed to determine the phase and chemical composition, structure, morphology [1], specific surface area, and textural characteristics of the samples.

The antimicrobial activity of the nanoparticles was tested on six Gram (-) (Aeromonas caviae, Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella enterica) and four Gram (+) bacterial species: Erysipelothrix rhusiopathiae, Bacillus subtilis, Bacillus cereus, Oerskovia paurometabola. The minimum inhibitory concentrations (MICs) of the materials against the test microorganisms were determined by the microdilution broth method.

The average MIC value is lowest for non-doped lavender-produced ZnO. The non-doped particles have a better effect than the doped ones. Among them, the Pr-doped sample, obtained with thyme essential oil, has the weakest effect. This may be due to the significantly larger atomic mass of praseodymium, which reduces the relative share of zinc oxide, the source of the antimicrobial effect. It is observed that MICs are higher in bacteria that have pathogenic potential. We assume that this effect is due to their better antioxidant protection, as it is a factor in the successful infection of the host, and the antimicrobial effect of metal oxide nanoparticles is due precisely to their ability to generate oxidative radicals.

Acknowledgments: Thanks the Bulgarian National Science Fund, KP-06-N69/8 (КП-06-Н69/8), “Novel polymer-hybrid materials containing (bio)synthesized metal oxide particles with improved photocatalytic and antimicrobial potential”, for the financial support and technical support from the project PERIMED BG05M2OP001-1.002-0005.

References

1. Ş. Ţălu, Micro and nanoscale characterization of three-dimensional surfaces. Basics and applications. Napoca Star Publishing House, Cluj-Napoca, Romania, 2015.