Rational Selection of Nanorod Plasmons: Material, Size, and Shape Dependence Mechanism for Optical Sensors

The localized surface plasmon resonance dependence on surrounding medium refractive index of Ag, Al, Au, and Cu nanoparticles is examined by electrodynamic approach. The refractive index sensitivity and sensing figure of merit (FOM) dependence of selected metal nanoparticles with similar geometry shows that although, sensing relevant parameters are shape (i.e., aspect ratio), and material dependent below the width 20 nm, but above this size these parameters are material independent under similar geometrical conditions. We have concluded that at optimum size, however, Al shows much higher refractive index sensitivity (RIS) in comparison to Au, Cu, and Ag, but FOM is higher for Ag in comparison to other metals. The observed sensing behavior is expected due to parameters like surface scattering, dynamic depolarization, radiation damping, and interband transitions, which may influence the nanorod plasmons.