Biomedical Engineering Reference
In-Depth Information
c
d
e
400 nm
100 nm
100 nm
Plasmon energy (eV)
b
f
3.0
2.0
3.5
2.5
1.5
1.0
0.5
UV
Visible
Near infrared
Mid infrared
400
500 600 800
1,000
3,000 9,000
Ag nanospheres
Wavelength (nm)
50 nm
20 nm
Au nanospheres
Nanoshells, nanoegg
a
g
Nanorods
Triangles
Cubes
Nanorice
50 nm
FIGURE 5.2
(See. color. insert.). Nanoparticle. resonance. range. of. plasmon. resonances. for. a. variety. of. particle. morphologies..
(©.2007.Macmillan.Publisher's.Ltd..Used.with.permission.).TEM.images.of.©.2004.(Au.spheres.(b)),.©.1995.(Ag.
spheres.(a)),.and.©.2001(SiO
2/
Ag.(core-shell).nanoshells.(c)),.and.SEM.images.of.©.2007.(nanorods.(d)),.©.2006.(cubes.
(e).and.nanorices.(g)),.American.Chemical.Society.and.©.2006.(triangles.(f))..(Wiley-VCH..Used.with.permission.)
and.shell-core.structures.have.also.been.demonstrated.
33,37
.Nanoshells.consist.of.a.spheri-
cal.dielectric.core.encased.in.a.metal.shell..The.core-shell.structure.has.tunable.plasmonic.
properties.highly.sensitive.to.the.inner.and.outer.shell.diameters,
38
.with.the.advantage.of.
extending.into.the.near.infrared.(NIR),.a.region.of.relative.transparency.for.living.tissues.
39
.
Nanorice.is.a.hybrid.nanostructure.combining.the.advantages.of.nanorod.anisotropy.and.
the. tunable. plasmon. resonances. of. nanoshells.
40
. Plasmon. resonance. tuning. occurs. by.
changing.the.nanorice.length.as.well.as.varying.the.relative.size.of.inner.and.outer.metallic.
shells..Branched.nanoparticles,.such.as.nanostars,.are.of.interest.due.to.their.sharp.edges.
and.can.exhibit.higher.SERS.intensity.at.the.tips.
41
.Since.the.LSPR.frequency.is.dependent.
on.both.the.shape.and.the.size.of.the.nanostructures,.the.wide.variety.of.NPs.mentioned.
above.can.have.their.LSPR.frequency.varied.from.the.entire.visible.to.mid-infrared.part.of.
the.electromagnetic.spectrum,.as.shown.in.Figure.5.2,.demonstrating.the.highly.tunability.
of.plasmonic.nanobiosensors,.which.enables.a.wide.variety.of.applications.in.biosensing.
5.3.2 Top-Down Nanofabrication
In.top-down.fabrication.of.LSPR.substrates,.NPs.are.condensed,.deposited,.or.grown.on.a.
supporting.substrate.such.as.silicon.wafers.and.glass.slides..Some.of.the.important.require-
ments.for.an.ideal.LSPR.substrate.in.practical.diagnostic.applications.are.that.the.substrate.
produces.a.high.enhancement,.generates.a.reproducible.and.uniform.response,.has.a.stable.
shelf-life,. and. is. easy. and. simple. to. fabricate.. Currently,. there. are. ive. major. fabrication.
techniques.that.could.potentially.produce.the.desired.nanoplasmonic.substrates.for.either.
