Size dependent structural, anti-bacterial and anti-biofilm properties of Er doped Li-Ni ferrites synthesized by the sol-gel auto-combustion route

The pure phased nanocrystalline Li0.25Ni0.5ErxFe2.25−xO4 (x=0.00, 0.04) ferrites were synthesized by the sol-gel auto combustion route and subsequently annealed at different temperatures. Thermal behavior of as-prepared materials was examined by the thermogravimetric and differential thermal analyzer (TG/DTA). The crystal structure, grain size and morphology were determined by using X-ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effects of the Er substitution as well as annealing temperatures on the structure, particle size and antibacterial properties were investigated. The antibacterial studies were carried out using both gram negative (Campylobacter jejuni, Enteropathogenic E. coli, Vibrio cholerae) and gram positive bacteria (Listeria monocytogenes and Staphylococcus aureus). The anti-biofilm activity of the doped nanocrystals was also evaluated. Doping of Er ions in Li-Ni ferrites enhanced antibacterial activity against the all tested bacteria. However, a marked decrease in the antibacterial activity of the doped nanocrystals was observed with the increase in the annealing temperature and the grain size. The significant reduction (P≤0.01) in the biofilm forming trends of all tested pathogens was noted when treated (doped nanocrystals) and untreated controls were compared. Campylobacter jejuni and Vibrio cholerae were found to be most susceptible to both the anti-bacterial (P≤0.01) and the anti-biofilm (P≤0.005) activities of the Li0.25Ni0.5Er0.04Fe2.21O4. The results indicated that Er doped Li-Ni nanoferrites can be used as a coating material to prevent the bacterial growth and the biofilm formation.