Plasmonic properties and electric field enhancement of core-shell Au@AgxAu1-x nanoshuttles embedded in water and in whole human blood

This study focuses on the analysis of the surface plasmon resonance (SPR) properties and electric field enhancement of core@shell nanoshuttles (Au@Ag x Au 1-x ), consisting of a gold (Au) nanorod core and a nanoshuttle-shaped alloy shell Ag x Au 1-x , embedded in water and in a biological medium. Finite Element Method (FEM) simulations are performed to investigate the effects of various parameters on the optical response of these nanoparticles (NPs), such as shell thickness, aspect ratio, alloy composition of the Ag x Au 1-x shell, and the polarization angle of the incident electromagnetic field. The results show strong tunability of the longitudinal SPR mode, which exhibits a pronounced redshift toward longer wavelengths as the shell thickness decreases, while the transverse mode is only slightly affected. The incorporation of silver (Ag) into the Au-shell significantly enhances the plasmonic performance and near-field enhancement capability, leading to higher absorption efficiency, improved field-map contrast in the vicinity of the NP, enhanced spectral tunability, and reduced plasmon damping compared to monometallic Au nanostructures. Furthermore, the SPR response exhibits a strong dependence on polarization, with maximum absorption occurring when the incident field is aligned with the longitudinal axis of the nanoshuttle. These results demonstrate the potential of Au@Ag x Au 1-x core–shell nanoshuttles as tunable plasmonic platforms for optical biosensing and surface-enhanced spectroscopic applications, motivated by their strong NIR absorption and pronounced near-field enhancement.