The shape-dependent optical properties of metal
nanostructures have motivated efforts to correlate
nanoparticle structure with plasmonic behavior. In
particular, gold bipyramids (BPs) are of interest due
to their sharp tips that lead to strong localized field
enhancement and high sensitivity to the surrounding
environment. However, despite their potential,
relatively few reports have studied the optical
properties of sub-100 nm BPs due to their relatively
low synthetic yields. To overcome this issue, density
gradient centrifugation has been used to isolate the
minority BPs from the rhombic dodecahedra (RD)
that are predominant following synthesis. The
resulting monodisperse BPs show 2.5 times higher
refractive index sensitivity than RD nanoparticles.
