Ultrastable graphene isolated AuAg nanoalloy for SERS biosensing and photothermal therapy of bacterial infection

Plasmonic metal nanomaterials with intrinsic surface–enhanced Raman scattering (SERS) and photothermal properties, especially AuAg nanoalloys with both the outstanding merits of Au and Ag nanocrystals, show huge application prospects in bacterial theranostics. However, the direct exposure of AuAg nanoalloys in external conditions probably cause undesirable reactions and poisonous metal ion leakage during SERS detection and photothermal antibacterial therapy process, which severely hinder bacterial theranostics applications. Herein, we report an ultrastable graphene–isolated AuAg nanoalloy (GAA) with AuAg core confined in few–layer graphitic shell as a versatile platform for bacterial detection and therapy. The encapsulation of graphene ensures the good stability of AuAg core, that its superior SERS and photothermal properties are therefore further guaranteed. GAA is used for SERS detection of two vital bacterial biomarkers (including corrosive cyanide and pyocyanin), exhibiting good SERS quantitative and multiplexing ability. GAA is further used for photothermal antibacterial therapy application, and ultrahigh antibacterial efficacies for both Gram–negative Escherichia coli and Gram–positive Staphylococcus aureus are achieved under 808 nm laser irradiation. This work proposes a valuable method to develop robust bacterial theranostic platform.