Optimization of the ultra-narrow plasmonic bandwidth of Pt-coated Au nanorod: The application in refractive index sensing

The refractive index sensitivity of Au nanorod with Pt coating has been studied theoretically. Calculation results based on quasi-static approximation show that Au–Pt core–shell nanorod exhibits higher refractive index sensing ability than bare Au nanorod without Pt coating. The refractive index sensitivity could be improved by increasing the aspect ratio of the inner Au nanorod or increasing the Pt coating thickness, and the maximum sensitivity can exceed 561 nm per refractive index unit. Because of the ultra-narrow plasmonic bandwidth, the Au–Pt core–shell nanorod also has large value of figure of merit. By increasing the Pt coating thickness or decreasing the aspect ratio, the figure of merit could be effectively improved to 7.45. The physical origin has also been investigated based on the geometry-dependent relaxation time and density of surface charges. These excellent refractive index sensing performances of Au–Pt core–shell nanorods present well potential for plasmonic sensing applications.