
702 Handbook of Biomedical Optics
extinction peaks. Gold nanocages, with their hollow interior,
have properties similar to gold nanoshells (Chen et al. 2005).
Gold nanorods have two extinction peaks, generally attributed
to the transverse and longitudinal plasmon modes. e trans-
verse peak is centered at 520 nm, near the peak for isolated gold
spheres, while the longitudinal mode shis toward the infrared
with increasing aspect ratios. Aggregates of plasmonic nanopar-
ticles have broad peak features that are highly dependent on the
specic aggregate morphology, but in general the extinction will
red-shi as the interparticle spacing