Bimetallic Silver–Gold Nanoplates for Photothermal Antimicrobial Therapy: Integrating High Efficiency with Stable and Multifunctional Design

Antimicrobial photothermal therapy requires nanomaterials that combine high plasmonic performance, colloidal stability, and scalable synthesis. In this work, we prepared bimetallic silver nanoplates partially coated with an ultrathin gold layer in a larger-volume batch (160 mL), while preserving stable optical properties and tunable photothermal performance in the biological near-infrared range. The resulting silver–gold nanoplates efficiently convert near-infrared light into heat and exert potent antimicrobial effects against Pseudomonas aeruginosa and Staphylococcus aureus. Systematic evaluation showed that thiol-terminated polyethylene glycol functionalization preserves the optical response of the nanoplates while improving colloidal stability in biologically relevant media. Furthermore, we investigated the trade-off between multifunctionality, stability, and photothermal efficiency observed after silica coating followed by covalent BSA conjugation, which increases surface functionalization versatility but reduces antimicrobial performance under the tested conditions. This work presents an efficient route to synthesize bimetallic Ag–Au nanoplates in large-volume batch for noninvasive antimicrobial photothermal applications and outlines key design principles to guide the development of next-generation multifunctional plasmonic nanoplatforms for antimicrobial therapy.