Silver Nanoparticles Embedded in Sodium Alginate: Antibacterial Efficacy and Effects on Red Cabbage Seedling Performance

Innovative plant protection solutions are increasingly sought in modern agriculture. Rapid advances in nanotechnology offer promising opportunities to develop biodegradable, cost-effective composites containing silver nanoparticles (AgNPs) with well-documented antimicrobial properties. The aim of this study was to synthesize sodium alginate gels containing AgNPs, evaluate their physicochemical and antibacterial properties, and assess their effect on the growth of red cabbage (Brassica oleracea var. capitata f. rubra) seedlings. In accordance with the principles of green chemistry, AgNPs were chemically synthesized using sodium alginate as a stabilizer and fructose as a non-toxic reducing agent. The final composite contained 150 mg/L AgNPs and was diluted to 20 and 60 mg/L for biological tests. Antibacterial activity against Bacillus cereus, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa was tested using agar diffusion assays. Seedling growth parameters and phytochemical content were assessed after 10 days of seedlings exposure to AgNPs. The results showed significant antibacterial activity in all tested strains. Crucially, neither AgNPs concentration negatively affected seedling development or phytochemical concentration. Application of AgNPs at concentration of 60 mg/L increased ascorbic acid and carotenoids content in comparison to control (deionized water). These results suggest that AgNPs-alginate composites may serve as sustainable antimicrobial agents in agriculture, inhibiting pathogens without compromising crop quality.