Correlation of optical sensing with extinction coefficient and local field enhancement in gold nanosphere dimer

Abstract

In this paper we systematically study the optical extinction, local field enhancement, and resonance peak shift of basic single/double gold nanosphere system. We find that in the double gold nanosphere system, the incident light can excite the coupled resonance modes when the two gold nanospheres are approaching to each other, leading the local field to be enhanced greatly. Interestingly, limited by the scant volume of local field, the extinction coefficient of the double gold nanosphere system of 2 nm gap with a high local field enhancement factor is greatly reduced, so that its optical sensing sensitivity and extinction coefficient are smaller than the 5 nm gap system’s. Studies show that the optical sensing sensitivity of the double gold nanosphere system is not directly determined by the local field enhancement amplitude, but has a similar change behavior to the extinction coefficient of the system. These results can offer us a useful route and hint for designing the gold nanoparticle systems used in the surface Raman scattering enhancement and high performance optical sensing.