Optimizing the figure of merit of gold nanoshell-based refractive index sensing

In this article, the dependences of the refractive index sensitivity, linewidth, and figure of merit on the geometrical parameters of gold nanoshells are investigated by using the Mie theory of a coated sphere with the size-dependent dielectric function of metal nanoparticles. It is found that the hollow gold nanoshell have higher refractive index sensitivity as compared to the silica–gold nanoshell of the same dimensions. In addition, increasing core radius or decreasing shell thickness leads to a great improvement in the refractive index sensitivity, but it results in an excessive broadening of the linewidth, which make the detection of the resonance wavelength changes difficult. Therefore, the figure of merit is calculated to find optimal dimensions for gold nanoshells having the best sensing performance. The results show that the maximal figure of merit for the hollow gold nanoshell (2.59) is a little greater than that for the silica–gold nanoshell (2.50), and the optimal core radius and shell thickness, corresponding to the maximal figure of merit, of the hollow gold nanoshell (silica–gold nanoshell) are 31 and 7 nm (29 and 8 nm), respectively. The optimized gold nanoshells can be treated as potential candidates for chemical and biological sensing.