Development of silver-zein composites as a promising antimicrobial agent

Recently, silver, a traditional broad-spectrum antiseptic, drew increasing attentions as a solution against antibiotic resistant bacteria. Various synthetic polymers and nature polymers were applied to form silver polymer composites to cope with the defects (e.g., low hemocompatibility) of silver-loaded antimicrobial agents. In this study, an alcohol-soluble prolamine, zein, was applied to prepare silver-zein composites as novel antiseptics. Both zein in silver (Z]A) and silver nanoparticles (AgNP) in zein (A']Z) structures at two pH conditions (i.e., pH = 3.3 and 6.5) were successfully prepared. Several characterization methods (i.e., zeta potential, FTIR, SEM, and turbidity) confirmed the formation of silver-zein composites through a nitrogen-silver coordination bond and electrostatic interaction. It was found that low pH was critical in facilitating formation and increasing stability of the silver-zein composites, probably by inducing electrostatic interaction between silver and zein. The antiseptic activities (i.e., growth inhibition and bactericidal activity) of different silver-zein composites were studied against Gram negative E. coli and Gram positive S. aureus . It was revealed that the silver-zein composites showed similar or better results against both types of bacteria compared to those of AgNO(3) and AgNP, except for the sample of A']Z-Ac. It had better growth inhibition activity but inferior bactericidal activity than that of AgNP because of its decreased solubility in aqueous medium. Furthermore, addition of zein was proven to be capable of dramatically increasing hemocompatibility of silver-loaded antiseptic agents. Therefore, silver-zein composites prepared in this work may find applications in wound care and food packaging areas.