On the Origin of the Plasmonic Properties of Gold Nanoparticles

Gold nanoparticles (AuNPs) are widely used as biological imaging agents, colorimetric sensors, surface-enhanced Raman spectroscopy (SERS) substrates, photothermal anti-cancer agents, visible wavelength photocatalysts, and photovoltaic materials. These applications are based on the plasmonic properties of AuNPs. Therefore, a fundamental understanding of the origin of the plasmonic behavior of AuNPs allows us to control the properties of AuNPs and widen their applications. In this review, we discuss the origin of the color, SERS, and hot-carrier generation of AuNPs. We start with the free-electron Drude model and the dielectric constant of AuNPs, which defines the material properties. We then explain the mechanism that determines the colors of bulk and nanosized gold, enhancement of the electric fields outside the AuNPs, and generation of hot carriers during the decay of plasmons.