Porous Au–Ag Nanoparticles from Galvanic Replacement Applied as Single‐Particle SERS Probe for Quantitative Monitoring

Abstract Plasmonic nanostructures have raised the interest of biomedical applications of surface‐enhanced Raman scattering (SERS). To improve the enhancement and produce sensitive SERS probes, porous Au–Ag alloy nanoparticles (NPs) are synthesized by dealloying Au–Ag alloy NP‐precursors with Au or Ag core in aqueous colloidal environment through galvanic replacement reaction. The novel designed core–shell Au–Ag alloy NP‐precursors facilitate controllable synthesis of porous nanostructure, and dealloying degree during the reaction has significant effect on structural and spectral properties of dealloyed porous NPs. Narrow‐dispersed dealloyed NPs are obtained using NPs of Au/Ag ratio from 10/90 to 40/60 with Au and Ag core to produce solid core@porous shell and porous nanoshells, having rough surface, hollowness, and porosity around 30–60%. The clean nanostructure from colloidal synthesis exhibits a redshifted plasmon peak up to near‐infrared region, and the large accessible surface induces highly localized surface plasmon resonance and generates robust SERS activity. Thus, the porous NPs produce intensely enhanced Raman signal up to 68‐fold higher than 100 nm AuNP enhancement at single‐particle level, and the estimated Raman enhancement around 7800, showing the potential for highly sensitive SERS probes. The single‐particle SERS probes are effectively demonstrated in quantitative monitoring of anticancer drug Doxorubicin release.