Facile solid-state synthesis and study in vitro of the antibacterial activity of NiO and NiFe2O4 nanoparticles

This paper presents the synthesis of NiO and NiFe2O4 nanoparticles (NPs), with an average crystallite size of 7 +/- 0.6 and 5 +/- 0.4 nm respectively, by a simple, low-cost, and environmentally friendly mechanochemical method. X-ray diffraction (XRD) patterns and high-resolution transmission electron microscopy (HR-TEM) reveal that NiO and NiFe2O4 NPs possess a cubic crystal structure. Their corresponding Raman scattering spectra confirm the structure and composition of these nanoparticles, and the band gap energy was determined from their Tauc's plot, being 3.44 eV for NiO and 1.55 eV for NiFe2O4. A strong confinement was observed for NiFe2O4 NPs because it exhibits a superparamagnetic behavior at room temperature. Besides, the antibacterial activity of these NPs against two opportunistic pathogens Pseudomonas aeruginosa (ATCC 43,636) and Staphylococcus aureus (ATCC 23,235), was tested in vitro. The results obtained from the microbroth dilution method showed that NiO and NiFe2O4 NPs inhibit 100% and 70% of the P. aeruginosa growth, respectively, while both oxides, inhibit 100% of S. aureus growth. The methodology presented in this work allowed us to obtain NPs with small size, low polydispersity, defined morphology, and is particularly suitable to produce other NPs of metal oxides.