Dynamic light scattering is a method that depends on the interaction of light with particles. This method can be used for measurements of narrow particle size distributions especially in the range of 2–500 nm. Sample polydispersity can distort the results, and we could not see the real populations of particles because big particles presented in the sample can screen smaller ones. Although the theory and mathematical basics of DLS technique are already well known, little has been done to determine its limits experimentally. The size and size distribution of artificially prepared polydisperse silver nanoparticles (NPs) colloids were studied using dynamic light scattering (DLS) and ultraviolet-visible (UV-Vis) spectroscopy. Polydisperse colloids were prepared based on the mixture of chemically synthesized monodisperse colloids well characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), DLS, and UV-Vis spectroscopy. Analysis of the DLS results obtained for polydisperse colloids reveals that several percent of the volume content of bigger NPs could screen completely the presence of smaller ones. The presented results could be extremely important from nanoparticles metrology point of view and should help to understand experimental data especially for the one who works with DLS and/or UV-Vis only.

Titanium dioxide coatings were prepared on Si wafers using the sol-gel method. Four different types of coatings with silver nanoparticles (AgNPs) were synthesized. The diameter and surface density of AgNPs were conditioned by the concentration of Ag + ions in the initial solution, time and UV illumination source. The bactericidal activity of AgNPs on the titanium dioxide coatings against the S. aureus strain were calculated as the percentage of the inhibition of bacterial growth after 24 hour incubation of microorganisms at 37 1C on TiO 2 coatings with AgNPs. Control samples were coated with titanium dioxide without AgNPs. We concluded that the titanium dioxide coatings modified with silver nanoparticles had a high antibacterial activity. Moreover, we demonstrated strong dependence between surface areas of AgNPs and inhibition of bacterial growth. The obtained results evidence that the surface area of AgNPs grown on titanium dioxide coatings is a major factor determining their antimicrobial potential.

No abstract

Nanomaterials with high stability and efficient antibacterial activity are of considerable interest. The preparation of silver nanoparticles (AgNPs) on titania coatings and their effective antibacterial activity against Staphylococcus aureus ATCC 6538 were reported. Titanium dioxide (TiO 2) coatings with AgNPs were prepared on Si wafers using the reactive magnetron sputtering method. The surface topography of AgNPs/TiO 2 coatings imaged using scanning electron microscopy revealed that the size and surface density of AgNPs grown by the photoreduction of silver ions were dependent on the concentration of AgNO 3 in the primary solution and the time of TiO 2 exposure to UV illumination. Evaluation of the antimicrobial properties and surface analysis before and after the biological test of AgNPs/TiO 2 coatings indicates their high antimicrobial stability and durability. Furthermore, the interdependence between the concentration of released silver and bacterial growth inhibition was demonstrated. In addition, direct contact killing and released silver-mediated killing have been proposed as a bactericidal mechanism of action of tested coatings with AgNPs.