Sensitivity of Localized Surface Plasmon Resonance (LSPR) Au Nanorod with Methylene Blue Medium Using Boundary Element Method Simulation

We have calculated the sensitivity of gold nanorod (AuNR) in water solution and methylene-blue based on boundary element method with varying diameter of the nanorod, D are 20 nm, 40 nm, 60nm, and 80 nm. The aspect ratio was varied from 1.5 to 3.5 according to diameter. The dielectric function of AuNR based on Christy and Johnson experiment. To understand the sensitivity sense, we have also varied the medium refractive index is n = 1.3334 (100% water pure) and n = 1.347 (100% methylene-blue pure). The sensitivity of LSPR Au nanorod was determined by the gradient of the peak of wavelength to the refractive index medium variation for all aspect ratio. The LSPR of AuNR consisted of a longitudinal and transversal mode. The longitudinal mode appeared higher wavelength than the transversal mode in LSPR spectra and the peak of wavelength increased as the aspect ratio increased while in transversal mode the peak of wavelength relatively was 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.