Optimization of the refractive index plasmonic sensing of gold nanorods by non-uniform silver coating

Localized surface plasmon resonance (LSPR) response sensitivity to the environmental refractive index (RI) has been studied for Ag coated Au nanorods both theoretically and experimentally. Quasistatic calculation results indicate that the Ag coating induced increasing of RI sensitivity only takes place when the Ag shell at the ends is much thicker than that at the side facets. Because of the corporate effects from the coating thickness dependent sensitivity and band width changing, the Ag coating always leads to an improvement of the figure of merit (FOM) of Au nanorod sensing, and the increase of FOM becomes faster as the Ag coating is non-uniform. Furthermore, higher RI sensitivity with the same resonance wavelength could be obtained by Ag coating, and the improvement of RI sensitivity with the same resonance wavelength could be fine tuned by changing the non-uniformity ratio of the Ag coating. These calculation results have also been verified experimentally. And this Ag coating dependent optimization of RI sensitivity of Au-Ag bimetallic nanorod makes them potential candidates for nanoscale biochemical sensing applications.