The Effects of Different Ionic Liquid Coatings and the Length of Alkyl Chain on Antimicrobial and Cytotoxic Properties of Silver Nanoparticles.

Introduction: The antibacterial efficacy and toxicity of silver nanoparticles (AgNPs) depends on their physicochemical properties including size, shape, surface charge and surface coatings. The Objectives of this study were: i) To synthesize and characterize positively charged AgNPs coated by different ionic-liquids with different alkyl chain lengths, ii) To evaluate the antimicrobial activity of these nanoparticles against Enterococcus faecalis compared to sodium hypochlorite (NaOCl) and chlorhexidine (CHX), iii) To compare the cytocompatibility of these solutions against L929 mouse fibroblasts.

Methods and Materials: AgNPs with positive surface charges capped by two different ionic liquids [imidazolium (Im) and pyridinium (Py)] with two alkyl chain lengths (C12 and C18 ) were synthesized. Im and Py were also tested as control groups. The characterization revealed synthesis of spherical NPs in the size range of 6.7-18.5 nm with a surface charge ranging from +25 to +58 mV. To standardize the comparisons, the surface charge to radius ratio of each nanoparticle was calculated. The minimum inhibitory concentrations (MIC) of the AgNP solutions, NaOCl and CHX were determined against E. faecalis by a microdilution test. An MTT-based cytotoxicity assay evaluated the cytotoxicity of the solutions in different concentrations on L929 fibroblasts. One-way and two-way ANOVA were used for statistical analysis.

Results: All tested AgNPs reached MIC90 in significantly lower concentrations compared to CHX and NaOCl. C12 Py-coated AgNPs had the lowest MIC90 value. CHX and NaOCl were more toxic on fibroblasts than all tested AgNPs. Im-coated AgNPs had better compatibility with fibroblasts than Py-coated particles; and C12 Im AgNPs had the best biocompatibility. Variations in alkyl chain length had no effects on the biocompatibility of AgNPs.

Conclusion: Py improved the antibacterial efficacy of AgNPs compared to Im; however, it had a negative effect on cytocompatibility. Alkyl chain length had no effects on AgNPs' bioactivity.