An investigation into the use of metal nanoparticles and their oxides as antimicrobial agents

Abstract

Nanotechnology is concerned with the study of processes and applications at the nanoscale (10-9 m), with objects that are generally smaller than 100 nm. Within the biomedical field, the use of metal nanoparticles and their oxides as antimicrobial agents is gaining attention. In this study, the potential antimicrobial activity of thirteen different nanoparticulate metals, oxides, carbides and nitrides was examined. These were generated by thermal plasma technology. Initially, ten different bacterial species/strains of clinical significance were subjected to in-depth antimicrobial screening, which included the determination of minimum inhibitory and minimum bacteriocidal concentrations. The nanoparticles that demonstrated the greatest potential as novel antibacterial agents were, in descending order of activity: Ag > CuO > Cu2O > Cu > ZnO with effective concentrations from 100 to 2500 μg/ml. Ag and CuO nanoparticles, alone and blended, along with the salts of both elements were further examined in time-kill assays. Nanoparticulate Ag (100 μg/ml) was able to reduce microbial populations to zero within 2h. While, nanoparticulate CuO required higher concentrations (> 1000 μg/ml) and longer times (up to 4h) than silver to reduce microbial populations to zero. Blends of Ag and CuO nanoparticles were shown to be superior than when used alone, with reduced concentrations and time required (approx. 50%). Nanoparticles alone were not shown to be superior to that of their corresponding salts. Antimicrobial activity in the presence of serum was not reduced. Nanoparticulate TiO2, which lacked antimicrobial activity in the absence of UV light, was shown to possess significant antimicrobial properties when irradiated with short wave radiation. Environmental Scanning Electron Microscopy (ESEM) and - 3 - Scanning Ion Conductance Microscopy (SICM) were used to examine toxic effects of nanoparticles on bacteria. These revealed CuO nanoparticles to cause a greater physical change to bacteria when compared to Ag. Following nanoparticle incorporation into epoxy resin and polyurethane, the antimicrobial activity of the resulting polymer-nanocomposites were examined. Both polymers were shown to exhibit antimicrobial properties. Ion release was shown to be more marked from materials containing CuO nanoparticles. Nanoparticle biocompatibility using skin, respiratory and gastrointestinal cell lines was also investigated. CuO was shown to be generally more toxic than Ag to eukaryotic cells.