Antibacterial, Redox, Cytotoxic, and Ecotoxic Properties of New Sol-Gel Silica-Copper-Based Materials

Objective: The objective of our study was to synthesize and characterize silica-copper nanomaterials and to evaluate their biological properties (antibacterial, redox, cytotoxic, and ecotoxic) for potential applications. Methods and Results: Si/Cu-based materials were prepared by a sol-gel method. They were characterized by XRD, UV-Vis, and SEM-EDS. The antibacterial activity of the materials was evaluated against Gram-positive bacteria (Staphylococcus aureus, Bacillus cereus), Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium), and yeasts (Candida albicans, Saccharomyces cerevisiae). The nanomaterial that was calcined at 500 °C exhibited greater antibacterial efficacy compared to the gel form. S. typhimurium demonstrated the highest susceptibility, whereas S. aureus and P. aeruginosa were the most resistant of the tested bacteria. Both yeasts exhibited comparable sensitivity (MBC = 1.0 mg/mL). The redox activity of both nanomaterials was tested at pH 7.4 (physiological) and 8.5 (optimal) by the activated chemiluminescent method. The nanocomposites significantly inhibited the free-radical and ROS generation. This presents them as redox regulators in living systems. The cytotoxic effects in normal BEAS-2B and tumor A549 human cell lines were assessed microscopically and by the cell viability neutral red uptake assay, CC₅₀ being evaluated. The observed effects suggest moderate, similar cytotoxicity in both cell lines. The ecotoxicity study using Daphnia magna showed an LC₅₀ of ~7-8 mg/L about Si/Cu/500. The LC₅₀ for Si/Cu (gel) was lower than 0.25 mg/L, indicating an increase in toxicity with increased exposure time. Conclusions: Possible applications of the newly synthesized nanomaterials include antimicrobial coatings, drug delivery systems, antioxidant additives in various formulations, and water purification.