Improve the plasmonic optical tunability of Au nanorod by Pt coating: the application in refractive index sensing

Plasmonic light absorption properties of bimetallic Au-Pt core-shell nanorod are investigated theoretically. The plasmonic absorption intensity comparison between the longitudinal peak corresponding to outer Pt surface (denoted as band Pt-L) and the transverse peak corresponding to Au-Pt interface (denoted as band Au-T) is sensitive to the environmental dielectric constant. By increasing the environmental dielectric constant, the band Pt-L fades down, whereas the band Au-T gets intense. So the absorption discrepancy between Pt-L and Au-T bands could be greatly enhanced by increasing the environmental dielectric constant, which is more sensitive to the environmental refractive index than single plasmonic band. This refractive index sensing based on two bands' absorption discrepancy could be further improved by increasing the Pt coating thickness or the aspect ratio of inner Au nanorod. The refractive index sensing based on red shift of the longitudinal peak corresponding to Au-Pt interface is also competitive, which can also be improved by increasing the Pt coating thickness or aspect ratio of inner Au nanorod. A mechanism based on media polarization-related electric field discontinuity and distribution of surface charge density was investigated to illuminate the absorption intensity-dependent refractive index sensing.

Automated summary

The plasmonic absorption properties of bimetallic Au-Pt core-shell nanorods were investigated theoretically, with a focus on the environmental dielectric constant's impact on the absorption intensity comparison between different peaks. Increasing the environmental dielectric constant can enhance the absorption discrepancy between the Pt-L and Au-T bands, improving refractive index sensing performance. This sensing can be further improved by increasing the Pt coating thickness or aspect ratio of inner Au nanorod.