DDA simulations of noble metal and alloy nanocubes for tunable optical properties in biological imaging and sensing

Abstract

The selection of nanoparticles for achieving efficient contrast in biological imaging and sensing is based on their optical properties. In the present study, discrete dipole approximation (DDA) simulated Ag, Au and their alloy nanocubes of various edge length spectra are used to investigate the surface plasmon resonance (SPR) wavelength, resonant line-width, relative contribution of scattering in extinction, and sensitivity of the SPR peak position to the refractive index of the embedding medium. The optical properties are significantly altered by the nanocube alloy composition. The scattering to absorption ratio is enhanced and tuned in the visible regime by alloying the metals, which may be useful for biological imaging. The sensitivity of the SPR peak position to the bulk refractive index is enhanced in alloys compared to pure metals. According to the sensing figure of merit (FOM), there exists an optimum alloy nanocube edge length and spectral region to obtain the best sensing performance. Such endeavours have the potential to improve the sensing performance of the nanoparticles with tunable SPR wavelength of the desired spectral regime.