They are quite different from the widely
investigated spherical gold nanoparticles (AuNp), [8] including
more distinguished physical properties [9] particularly for their
tunable absorption in the visible and near infrared region. When
a nanosize metal particle is activated by light, the collective oscillation
of conduction electrons occurs on the particle surface, which
is called localized surface plasmon resonance (SPR) [10,11]. It
exhibits unique phenomena such as intense absorption at a wavelength
resonant with the electronic transition of molecules in the
ultraviolet–visible (UV–Vis) region. While the analogies between
nanoparticulate building blocks at the nanoscale and the atomic building blocks at the molecular-scale appear appealing, [12,13] it
must be remembered that nanoparticles-unlike atoms, are never
mono dispersed, and no two particles are ever identical. This inherent
polydispersity proves self-assembly, and affects the overall
characteristics deriving from the size-dependent properties of
individual NPs (e.g., SPR) [14,15] or magnetic susceptibility [16,17].