Positively charged imidazolium-based ionic liquid-protected silver nanoparticles: a promising disinfectant in root...

To synthesize and characterize silver nanoparticles (Ag NPs) with different surface charges in order to evaluate their cytotoxicity and antibacterial activity in the absence and presence of dentine compared with NaOCl and CHX.

Ag NPs with positive, negative and neutral surface charges were synthesized and characterized. The first phase of the experiment determined the minimum inhibitory concentrations (MICs) of NPs against planktonic E. faecalis and compared them with that of NaOCl and CHX. The second phase tested the elimination of E. faecalis at different contact times (5, 20 and 60 min and 4 and 24 h), and the role of dentine in their inactivation was assessed. In the third phase, the most effective Ag NP solution was selected for cytocompatibility assessment. An MTT-based cytotoxicity assay was used to evaluate the cytotoxicity of the selected NP solution in different concentrations on L929 fibroblasts compared to that of 2.5% NaOCl and 0.2% CHX. Student's t-test and repeated measures manova approach were used for statistical analyses.

The characterization revealed synthesis of colloidal NPs in the size range of 5-10 nm in diameter. The results indicated that Ag NP with a positive surface charge had the smallest MIC against planktonic E. faecalis, and it was active in very lower concentrations compared to NaOCl, CHX and the other tested AgNPs. Positive-charged Ag NPs at 5.7 × 10(-10)  mol L(-1) completely prevented the growth of E. faecalis after 5 min of contact time, a finding comparable to 0.025% NaOCl. Dentine powder had variable inhibitory effects on all tested materials after 1 h incubation period, but after 24 h, NaOCl and the positive-charged Ag NPs were not inhibited by dentine at any concentration used. CHX was the most and the positively charged Ag NP solution was the least toxic solutions to L929 fibroblasts (P < 0.001).

Ag NP surface charge was important in bactericidal efficacy against E. faecalis. The positively charged imidazolium-based ionic liquid-protected Ag NPs showed promising antibacterial results against E. faecalis and exhibited a high level of cytocompatibility to L929 cells.