“9.61x6.69” b2815 Tissue Engineering and Nanotheranostics
Plasmonic Nanoparticles Application in Biosensor and Bioimaging 159
The nanoparticle’s refractive index sensitivity (S), reported in
nanometers of peak shift per refractive index unit (nm/RIU), repre
sents its sensitivity as plasmonic effect and is various for different
materials.
p.
d
S
dn
λ
=
(18)
For example, the refractive index sensitivity S of gold nanospheres
with 50 nm in diameter is 60 nm/RIU,^17 while silver nanosphere
with same size is about 160 nm/RIU.^18 As another example, refrac
tive index sensitivity of gold nanocubes with 30–50 nm in size is
83 nm/RIU^19 while 146 nm/RIU^20 for silver nanocubes in the same
size. These results indicate that the scattering light of Ag nanosphere
is much more sensitive for environment change than gold nano
sphere. Meanwhile, nanoparticle’s refractive index sensitivity also
relates with its shape. It is discovered that silver nanotriangles had
a much higher sensitivity (350 nm/RIU) than that of spheres
(160 nm/RIU).^18 As the refractive index sensitivity directly deter
mines the sensitivity of sensors to engineer novel sensor with high
sensitivity and specificity, much effort has been spent in studying the
relationship between refractive index sensitivity and the structure of
plasmonic nanoparticles. In briefly, particles with sharp tips (nanotri
angles, bipyramids) exhibit especially high refractive index sensitivi
ties. For example, Sun et al. demonstrated that gold nanoshell has a
much higher S (409 nm/RIU) than that of nanosphere (60 nm/
RIU) in the same diameter.^17 For gold nanorods (AuNRs), Lee et al.
showed that the sensitivity increases from 157 nm/RIU to 497 nm/
RIU for aspect ratio increasing from 1.0 (spheres) to 3.4.21–23
3. Fabrications of Plasmonic Nanoparticles
LSPR, associated with noble metal nanostructure, results in a strong
oscillation of its surface electrons and creates strong electromagnetic
nearfield enhancement as well as sharp spectral absorption and scat
tering peaks when its electric field resonates with a certain wavelength
