Microfluidics for Biosensor Chips - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 141

the purpose of precise liquid delivery. 16,17 Gold nanoparticles are
synthesized in a solution and immobilized on the quartz slide. One
self-assembled thiol-based monolayer covers the nanoparticles to
functionalize with antigen probes such as biotin molecules. A light-
emitting diode (LED) light source irradiates through the slide to
interrogate the changes of dielectric properties due to the binding
of antibodies with the immobilized antigens. This type of biosensing
chip has demonstrated a 270 ng/mL detection limit using anti-
biotins samples, which is comparable with the limit using a Biacore
SPR sensing chip.
Nanosphere lithography has been used to craft nanoparticle
arrays on membrane substrates, in which Ag nanoparticles
are orderly arranged. Cytochrome P450 enzymes, which prevent
the nanoparticles from their inherent aggregation properties, are
stabilized on the particle surface to study drug binding mechanisms
via monitoring the shifts of the PPR spectrum. 18
When these functionalized nanoparticles are coated on optical
waveguide substrates, such as planner waveguides or optical ibers,
the attenuated intensity of guided light due to PPR interactions
with the nanoparticles can be used to determine speciic sensing
events on the particles. Chapter 5 discusses PPR biosensing
applications using waveguide-based devices. Due to miniaturizing
waveguide devices requiring less effort, developing microluidic
chips using waveguide-based PPR sensing is more straightforward
than developing SPR chips.
For instance, one segment of plastic buffer wrapping optical
iber can be removed to coat Au nanoparticles on the cladding
layer. An LED or laser light coupled into the iber propagates
along the iber via internal relection. As described in the previous
section, the light attenuation due to relection along the iber is
sensitive to the permittivity change of coated nanoparticles. When
recognition probes are implanted on the particles coated on the
iber suspended in one low cell, the intensity attenuation or PPR
scattering wavelength shift can report the binding events of targets
in sample solutions. Various assays using iber optic-PPR (FO-PPR)
systems have been developed to detect anti-DNP and anti-nuclear
antibodies. 19,20 The size of FO-PPR low cells can be reduced to a sub-
mm scale to become microluidic devices saving the consumption of
reagents and samples and shortening PPR signal response time due
to smaller diffusion distance from the iber surface.