Biomedical Engineering Reference
In-Depth Information
Analytes of interest
Bioreceptors
Detector
Scattering (E
s
)
E
0
Z
Absorption (E
ab
)
Dielectric
SPP
H
y
E
Plasmonic
nanoparticles
Optical
excitation
Enhanced local
near field (E
s
)
X
Incident light
Metal
Optical
excitation
Reflection
Extinction (E
ex
) = E
s
+ E
ab
Ѳ
Detector
Au-Ph
Au-Ph-DNA
1.0
0.8
1
0.6
Before binding
0.4
0.2
0.5
After binding
0
0.0
500
550
600
650
50 70
Incidence Angle Ѳ (degrees)
90
Wavelength (nm)
(a)
(b)
FIGURE 5.1
(a). A. typical. experiment. setup. (top). using. surface. plasmon. polaritons. (or. propagating. plasmon). and. a. resulting.
relectivity.spectrum.(bottom).obtained.in.an.angle-solved.mode..(b).A.typical.measurement.setup.(top).using.local-
ized. surface. plasmons. and. a. resulting. scattering. spectrum. in. biosensing. (bottom).. Au-Ph:. phosphine-coated. Au.
nanoparticles.(NPs),.in.which.a.surfactant.phosphine.was.used.to.solubilize.naked.Au.nanoparticles.in.aqueous.
solution.
interactions.”
12
. One. of. the. major. subields. of. nanophotonics. is. plasmonics,. in. which.
manipulation.of.light.is.based.on.interaction.processes.between.electromagnetic.radia-
tion.and.free-electron.plasma.(or.conduction.electrons).at.dielectric-metal.planar.inter-
faces.or.nanocurved.interfaces,.resulting.in.surface.plasmon.polaritons.(SPPs).or.localized.
surface.plasmon.polaritons.(LSPs),
13
.respectively..A.plasmon.is.a.quantum.quasi-particle.
representing. the. elementary. excitations,. or. modes,. of. the. charge. density. oscillations.
in. a. free-electron. plasma.
14
. As. shown. in. Figure. 5.1a,. SPPs. are. propagating. dispersive.
electromagnetic. (EM). waves. coupled. to. the. electron. plasma. of. a. conductor. at. the. pla-
nar.interface.between.dielectric.and.metal.materials,.having.a.combined.EM.wave.and.
surface.charge.character..The.surface.charge.is.generated.by.the.electric.ield.normal.to.
the.surface,.while.the.EM.waves.propagate.in.the.
x
.direction.(
H
.is.in.the.
y
.direction).for.
distances.on.the.order.of.tens.to.hundreds.of.microns..This.combined.character.leads.to.
the.ield.component.normal.to.the.surface.being.enhanced.near.the.surface.and.decaying.
exponentially. with. distance. in. the.
z
. direction. on. the. order. of. 200. nm.
15
. The. enhance-
ment.reaches.its.maximum.when.SPPs.resonate.with.the.incident.exciting.laser,.which.
is. called. surface. plasmon. resonance. (SPR),. corresponding. to. the. minimum. relectivity.
as.shown.in.Figure.5.1a.
