Silver-titanium dioxide nanocomposites as effective antimicrobial and antibiofilm agents

Ag-TiO2 nanocomposites were successfully developed from colloidal suspensions containing 750 or 1,500 ppm silver nanoparticles (AgNPs) deposited on 5 % (w/v) titanium dioxide nanoparticles (TiO(2)NPs) by a chemical reduction approach. The nanocomposites were characterized by diffuse reflectance UV-Vis spectroscopy (DRS), transmission electron microscopy (TEM), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) and dynamic light scattering (DLS). DRS spectra showed an absorption band in visible region with maximum absorbance peaks at 452 and 444 nm attributed to AgNPs plasmon peaks, indicating the formation of small spherical or quasi-spherical Ag nanocrystals in nanocomposites. TEM and SEM analysis proved a nearly spherical morphology of particles (15-30 +/- 5 nm average size in diameter). EDX analysis revealed the presence of Ti, O, and Ag in both nanocomposite powders having 1.37 or 2.34 wt% Ag content. DLS analysis yielded a bimodal particle size distribution in a narrow range (31.3 +/- 0.5 or 23.4 +/- 0.4 nm average particle diameter) and a good polydispersity (0.247 or 0.293 polydispersity index). The nanocomposites were screened for their in vitro antimicrobial activity against Gram-positive (Bacillus subtilis and Staphylococcus aureus) and Gram-negative (Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa) bacterial and fungal (Candida albicans) reference and clinical strains, in planktonic and adherent state, by qualitative and quantitative assays. The antibacterial activity increased with the increasing AgNPs content, being more intensive for Gram-positive bacteria. Both Ag-TiO2 nanocomposites exhibited a high antibiofilm activity. The obtained results recommend the use of the developed nanocomposites as antimicrobial and antibiofilm agents in practical applications without UV irradiation. The most effective agent proved to be the one with 2.34 wt% AgNPs content.