Abnormally Large Plasmonic Shifts in Silica-Protected Gold Triangular Nanoprisms

The synthesis of silica-encapsulated gold nanoprisms (AuNP@SiO2) is reported. These nanostructures are remarkably stable and resist etching and rounding of their sharp vertices (a process which begins on unprotected Au nanoprisms in a matter of hours) in many chemical environments (water, ethanol, dimethyl sulfoxide, and tetrahydrofuran). The silica growth process has been studied and occurs according to the shape of the particle, where the edges of the prisms are coated less than the large triangular facets. The AuNP@SiO2 particles have dielectric sensitivities that are as large as 737 nm/RIU. Discrete dipole approximation calculations have been used to investigate the effects of this variable thickness on dielectric sensitivity and show that for the anisotropic coatings it is significantly higher than for a uniform coating due to the location of electromagnetic hot spots near the tips and edges of the particles. These calculations also show that dipole resonances exhibit greater sensitivity than multipole resonances, due to the shorter range of the multipolar electromagnetic fields.