The antibacterial effect of ZnO nanoparticles is tested against Staphylococcus aureus, (a Grampositive pathogenic bacterium) from a particle-size, concentration, and surface-defects point of view. Activation of antibacterial activity was achieved by standard well diffusion agar and minimum inhibitory concentration procedures. Our results show that smaller-sized particles are more effective inhibitors of bacterial activity when used in a certain optimum concentration. To reveal the underlying mechanism of the observed size and concentration-dependent bacterial activity inhibition, we measured the concentrations of Zn 2+ ions released in each suspension by an inductive couple plasma optical emission spectrophotometer. Additionally, photoluminance spectra of our samples show significant surface defects (mainly oxygen vacancies) that generate reactive oxygen species. The underlying mechanism of the observed size-and concentration-dependent bacterial activity inhibition is attributed primarily to the release of Zn 2+ ions and generation of reactive oxygen species that interact and penetrate the cell membrane, causing lethal damage to the cell. Finally, the antibacterial effectiveness and maximum sensitivity of our nanoparticles is confirmed by optical density measurements. Keywords Zinc oxide. Reactive oxygen species ROS. Zn 2+ ion release. Antibacterial activity mechanism. Nanoparticles

The effects of surface defect (oxygen vacancies) on the electronic structure and photoluminance

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Cobalt (Co) doped magnesium hydroxide Mg(OH)2 nanoparticles are synthesized by a surfactant-free co-participation method. Scanning electron microscopy (SEM) images show nanometer size Mg(OH)2 particles in spherically shaped particle-like morphology. Synthesis of these Mg(OH)2 nanocrystals involves the formation of monomeric MgOH[Formula: see text] ions as the precursor for the Mg(OH)2 nuclei which finally evolves in spherical particle-like morphology. X-ray diffraction (XRD) confirms the hexagonal crystal structure of the samples. With increasing Co concentration, the absorption spectra of the samples show narrowing of the bandgap from 5.47 eV (for pure Mg(OH2)) to 5.26 eV (for 10% Co-doped Mg(OH2)) effect is attributed to changes in the interaction potentials between Co and the host Mg(OH)2 lattice due to dopant-induced lattice distortion and the presence of a mixed valance Co[Formula: see text]/Co[Formula: see text] state.