Tuning carbonyl precursors in chitosan-based Schiff base composites as capping agents for silver nanoparticles to enhance antibacterial activity

In this study, chitosan was chemically modified with salicylaldehyde, piperonal and furfural to synthesize Schiff base derivatives, which were subsequently used as stabilizing agents for silver nanoparticles (AgNPs). The aim of this research was to evaluate the effect of Schiff base structure on the size, stability and antibacterial activity of the resulting AgNPs composite. UV–Vis spectroscopy showed that the chitosan–salicylaldehyde/AgNPs (CsS-Ag) composite had the lowest Surface Plasmon Resonance (SPR) peak at 410 nm, indicating the smallest and most stable nanoparticles, attributed to strong bidentate coordination from the imine (-C=N) and ortho-hydroxyl (-OH) groups. In contrast, the chitosan–piperonal/AgNPs (CsP-Ag) exhibited the highest SPR peak at 481 nm, suggesting larger, less stable nanoparticles, while chitosan–furfural/AgNPs (CsF-Ag) showed an intermediate SPR at 439 nm, likely stabilized by π-π interactions. FTIR analysis confirmed the involvement of the imine group and nearby electronegative substituents in AgNPs coordination. Antibacterial testing using the Total Plate Count (TPC) method revealed that all Schiff base–AgNPs composites outperformed unmodified chitosan and Schiff bases alone. The CsS-Ag composite showed the strongest activity, reducing bacterial colonies by 98.89% on day 3 and 98.64% on day 7. These findings highlight the critical role of Schiff base structure in AgNPs stabilization and antibacterial performance.