Biomedical Engineering Reference
In-Depth Information
the conduction of electrons in crystalline solids. This periodicity strengthened by
Bloch state, significantly enhances the detection capability by fine-tuning several
parameters for the photonic crystal. According to Bloch state, the energy eigenval-
ues can be depicted as below:
ε
()
k
=
ε
(
kK
+
)
n
n
where
K
stands for periodicity of the reciprocal lattice vector (Fig.
11.12
).
The unique eigen-states become very effective in resonance mode. The reso-
nance mode can be modulated when refractive indices of the surrounding environ-
ments changes or the analyte is absorbed on a sensing surface, by changing the
resonance condition of the Fabry-Perot microcavity:
2
π
2
nd
cos
θα π
+= +
(2
m
1)
where
(
m
=
0,1, 2,....)
λ
α stands for the
Goos-Hänchen
phase shift between sensing surface and bulk envi-
ronmen, θ for the incident angle of the beam, n for the refractive index.
Because of its extreme sensitivity, it has been used to build a general-purpose
platform for label-free and fluorescent assays [
121
-
123
]. The Cunningham research
laboratory develops a method to investigate alterations of cell adhesion induced
on photonic crystal sensors by exposing them to drugs with selective activation of
a sub-class GPCR. Schematics of commercial photonic crystal product and their
mechanisms are shown in Fig.
11.11
. BIND® (SRU Biosystems) employs photonic
crystal structures to provide sensitive measurements of changes in binding or adher-
ence adjacent to the BIND Biosensor surface. These biosensors incorporate a novel
nanostructured optical grating which reflects a narrow range of wavelengths of il-
luminating light with broadband light. BIND is able to test numerous biomolecular
interactions including receptor activation, cell adhesion, protein-protein binding
and so forth. Specifically, they have demonstrated a GPCR subtype (G
i
, G
q
, G
s
,
G
12/13
coupled) activation based on a variety of cellular responses including calcium
mobilization, β-arrestin localization or second messenger levels.
Corning Corporation have also developed an EPIC® system for a high-through-
put label-free screening platform based on optical biosensor technology [
120
].
Numerous applications on cell-based GPCR assays can be found [
124
-
126
] and
compared to other label-free detection methodologies to provide interesting side-
to-side evaluation [
127
,
128
]. Fang et al. organized a list of publications regard-
ing a label-free optical biosensor utilizing resonant waveguide gating for whole
cell GPCR assays [
129
,
130
]. These optical waveguide structures are fabricated
by technologies based on microelectromechanical systems (MEMS); therefore it
can be easily integrated with microfluidics for precise analyte controls over the
optical waveguide. Many types of the microfluidic and nanofluidic systems have
shown its compatibility with a variety of MEMS (i.e. electrochemical pump [
131
],
microheater [
132
], NEMS resonator [
133
] etc.). In addition, a wide range of these
micro and nanofluidic system (down to few nanometer [
88
]) will allow the same
scale analysis of analytes incorporated onto this optical waveguide or any MEMS
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