Configuring Au and Ag nanorods for sensing applications

We have studied optimum configurations of Au and Ag nanorods for optical sensing applications. From the analysis of the resonance condition by means of the quasistatic approximation, it was found that sensitivity is controlled by two main factors: the aspect ratio of the nanorods and their composition (the metal’s bulk plasma wavelength), and it depends linearly on both. The finding was confirmed quantitatively using T-matrix calculations, even for particles with a radius of 40 nm, where the quasistatic approximation is no longer valid. For ease of detection, the intensity of the surface plasmon resonance band of the nanostructures was included along with its full-width at half-maximum in the correction factor C, which on multiplying with the sensitivity (ΔλSPR/Δnm) gives a figure of merit. It has been demonstrated that the metal nanorods, especially the larger ones, have better optical sensitivity than the nanostructures of nanobox- or nanoshell-like geometries, which have been reported to be the best optical sensors for these metals.