The sensitivity calculation of localized surface plasmon resonance (LSPR) Au nanorod by applying a boundary element system simulation

In this study, we have calculated the sensitivity of localized surface plasmon resonance (LSPR) Au nanorod by a public metallic particle simulation based on the boundary element method (Metallic Nano-Particle Boundary Element Method, MNPBEM). The diameter of nanorod D is 20 nm, 60 nm, and 80 nm. The variation of aspect ratio is 1.5 to 3.5. The dielectric of Au nanorod based on the Christine-Johnson experiment. To understand sensitivity sense, we have also varied the refractive index medium by Lorentz-Lorentz approximation from a mixture of water and glycerol concentration. The refractive medium index is n = 1.3334 (100 % water pure), n = 1.3605 (80 % water and 20 % glycerol), n = 1.3881 (60 % water and 40 % glycerol), n = 1.4164 (40 % water and 60 % glycerol), and n = 1.4452 (20 % water and 80 % glycerol). From MNPBEM simulation, we have produced LSPR spectra such as absorption, scattering, and extinction curve as the function of wavelength. Then, the sensitivity of LSPR Au nanorod is determined by the gradient of the peak of wavelength to the refractive index medium variation for all aspect ratio. Interestingly, we have found the LSPR Au nanorod consisted of longitudinal and transversal mode in LSPR Au nanorod curve. The longitudinal mode appeared a higher wavelength than the transversal mode in LSPR spectra. In longitudinal mode, the peak of wavelength increased as the aspect ratio increased (red-shift) while in transversal mode, the peak of wavelength was relatively constant. Furthermore, the sensitivity in longitudinal mode increased as the aspect ratio increased, whereas the sensitivity in transversal decreased as the aspect ratio increased. Increasing the sensitivity in longitudinal mode related to red-shift as the nanorod volume increased and the refractive medium index change. According to the results, the sensitivity determination is useful to understand the refractive index medium changes that it is important to design a sensor device.