Slide- and Micoarray-Based Biosensors Using Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 61

scattering) spectrum at wavelengths determined by the size, 17
shape, 18 or arrangement 19,20 of the nanostructures. An example of
various morphologies and their corresponding LSPR spectra are
shown in Fig. 4.3. The sensitivity of LSPR-based sensors in terms of
the changes in peak position and peak magnitude upon variations in
bulk or interfacial refractive index varies with these parameters. 17,18
This interfacial phenomenon is analogous to conventional PSPR, and
has been utilized to determine biomolecular binding on the surface
of a colloid in suspension. 21,22

4.3 Slide-Based LSPR Biosensors

For the development of a LSPR biosensor fabricated in a planar,
slide-based format using immobilized NMNPs on an optically
transparent substrate, there are, in general, three advantages for
this purpose. First, because most of, NMNPs permit the transmission
of light in the visible region of the electromagnetic spectrum, in
principle, a slide-based LSPR sensor should enable LSPR to be
performed in transmission mode or relection mode by a UV-visible
spectrophotometer. Second, LSPR biosensing can be performed with
nanostructures on solid surfaces to avoid the need to control the
delicate balance between keeping the biofunctionalized particles
in aqueous solution for measurements and aggregation of particles
due to biomolecular interactions since extensive biomolecular
interactions may cause gradual sedimentation of the particles over
time. Third, slide-based sensor can be designed in an array format
for rapid, high-throughput screening of biomolecular interactions.
A biorecognition couple, biotin-streptavidin, was the model
couple for creating a ligand-receptor binding reaction in a LSPR-
based biosensor. In one of these examples, biotin was attached to
13 nm diameter Au nanospheres (AuNPs) which were previously
immobilized on a glass substrate through an amino or mercapto
functionalized silane linker (see Fig. 4.4). 23 Local refractive index
changes induced by the binding of streptavidin were monitored
via the UV-vis spectral changes in transmission mode. This
spectrophotometric sensor shows concentration-dependent binding
and a detection limit of 16 nM for streptavidin. Upon optimization of
the size of AuNP, it has been found that the LSPR sensor fabricated
from 39 nm diameter AuNPs exhibits maximum sensitivity to the