Enhancing antibacterial activity of chitosan surface by heterogeneous quaternization

This research aimed to increase the antibacterial activity of the chitosan surface by introducing quaternary ammonium groups via a heterogeneous two-step process: reductive alkylation using a series of different aldehydes followed by methylation with methyl iodide. ATR-FTIR and XPS analyses, together with water contact angle and zeta potential measurements, confirmed the success of the surface quaternization. The antibacterial activity of the surface-quaternized chitosan film against Staphylococcus aureus and Escherichia coli, as model Gram-positive and Gram-negative bacteria, respectively, were superior to that of the virgin chitosan film. The apparent damaged bacterial morphology upon contact with the surface-quaternized chitosan film was verified by SEM. Thus, the introduction of additional positive charges to the chitosan surface via the versatile and yet simple process of heterogeneous quaternization can significantly improve the antibacterial activity of the chitosan surface, especially in a neutral environment.