Versatile roles of silver in Ag-based nanoalloys for antibacterial applications

Currently, indiscriminate use of traditional antibiotics drives the rapid evolution of multidrug-resistant pathogenic bacteria. Silver has been regarded as antimicrobial agent since ancient times, while silver nanostructures can treat bacteria through multiple interaction mechanisms, such as enhanced targetability, augmented drug loading efficiency and tunable physiochemical property. Generally, nano-silver with small sizes can eliminate pathogenic bacteria more efficiently, while it tends to aggregate, causing instability. After the formation of alloys with other noble metal elements such as gold, platinum, palladium, the stability of these nanomaterials can be significantly enhanced, with antibacterial activity maintained. Therefore, in this review, we focus on the roles of silver in Ag-based alloy nanostructure for antibacterial activity, according to the following mechanisms: the release of Ag+ ions to directly disturb the bacterial metabolism, the assistance to modulate surface plasmonic resonance adsorption of Ag-alloys to realize near infrared phototherapy, and the combination with Pt or Pd to the production of catalyze reactive oxygen species under bacterial microenvironment. Based on these understandings, we will summarize some common antibacterial disciplines for Ag-based nanoalloys, which may guide the further investigation for efficient antibacterial applications.