Silver Nanocluster-Embedded Zein Films as Antimicrobial Coating Materials for Food Packaging

Highly efficient antimicrobial agents with low toxicity and resistance have been enthusiastically pursued to address public concerns on microbial contamination in food. Silver nanoclusters (AgNCs) are known for their ultrasmall sizes and unique optical and chemical properties. Despite extensive studies of AgNCs for biomedical applications, previous research on their application as antimicrobials for food applications is very limited. Here, for the first time, by incorporating AgNCs (∼2 nm in diameter) into zein films that are widely used as food packaging materials, we developed a novel coating material with potent antimicrobial activity, low toxicity to human cells, and low potential to harm the environment. In addition, we systematically evaluated the antimicrobial activities and cytotoxicity of AgNCs-embedded zein films and compared them to zein films embedded with AgNO₃ or Ag nanoparticles with diameters of 10 and 60 nm (AgNP10 and AgNP60, respectively). At equivalent silver concentrations, AgNCs and AgNO₃ solutions exhibited considerably higher antimicrobial activities than those of AgNP10 and AgNP60 solutions. Moreover, AgNCs exhibited less cytotoxicity to human cells than AgNO₃, with a half maximal inhibitory concentration (IC₅₀) of 34.68 μg/mL for AgNCs, compared to 9.14 μg/mL for AgNO₃. Overall, the novel AgNCs coating developed in this research has great potential for antimicrobial applications in food packaging materials due to its high antimicrobial efficacy, ultrasmall size, and low cytotoxicity.