Effect of silver nanomaterials on the activity of thiol-containing antioxidants

The use of nanomaterials in consumer products is rapidly expanding. In most studies, nanomaterials are examined as isolated ingredients. However, consumer products such as foods, cosmetics, and dietary supplements are complex chemical matrixes. Therefore, interactions between nanomaterials and other components of the product must be investigated to ensure the product's performance and safety. Silver nanomaterials are increasingly being used in food packaging as antimicrobial agents. Thiol-containing compounds, such as reduced glutathione (GSH), cysteine, and dihydrolipoic acid, are used as antioxidants in many consumer products. In the current study, we have investigated the interaction between silver nanomaterials and thiol-containing antioxidants. The selected Ag nanomaterials were Ag coated with citrate, Ag coated with poly(vinylpyrrolidone), and Au nanorods coated with Ag in a core/shell structure. We observed direct quenching of the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) by all three Ag nanomaterials to varying degrees. The Ag nanomaterials also reduced the quenching of DPPH by GSH to varying degrees. In addition, we determined that the mixture of GSH and Au@Ag nanorods held at 37 °C was less effective at quenching azo radical than at ambient temperature. Furthermore, we determined that Au@Ag nanorods significantly reduced the ability of GSH and cysteine to quench hydroxyl and superoxide radicals. The work presented here demonstrates the importance of examining the chemical interactions between nanomaterials used in products and physiologically important antioxidants.