Biomedical Engineering Reference
In-Depth Information
5.6 Summary
Plasmonic. nanobiosensors. are. built. on. the. synergetic. combination. of. plasmonic. nano-
structures,. plasmonics,. and. surface. biofunctionalization.. The. resonant. electromagnetic.
behavior.of.noble.metal.NPs,.so-called.plasmonic.behavior,.is.due.to.the.coninement.of.
the. conduction. electrons. to. the. small. particle. volume.. Exquisite. control. synthetic. and.
fabrication.of.plasmonic.nanostructures.in.combination.with.advances.in.theory.and.the.
emergence.of.quantitative.electromagnetic.modeling.tools.have.provided.a.better.under-
standing.of.the.optical.properties.of.isolated.and.electromagnetically.coupled.nanostruc-
tures.of.various.sizes.and.shapes..This.better.understanding.of.plasmonics.enables.us.to.
more.effectively.design.and.synthesize.plasmonic.nanostructures.that.it.the.need.of.dif-
ferent.applications..Plasmonic.nanostructures.offer.an.extremely.sensitive.response.to.the.
dielectric.change.of.the.environments.within.tens.of.nanometers.from.the.nanomaterial's.
surface..Surface.biofunctionalization.integrates.unique.recognition.properties.of.biorecep-
tors.with.unique.optical.properties.of.plasmonic.nanostructures.to.make.the.nonspeciic.
but.sensitive.dielectric.response.speciic.to.the.analyte.of.interest..Furthermore,.the.biore-
ceptors.(e.g.,.enzymes,.antigens,.and.antibodies).have.dimensions.in.the.range.of.2-20.nm,.
similar.to.those.of.nanostructures,.indicating.that.the.two.classes.of.materials.are.structur-
ally.compatible..The.size.of.the.bioreceptors.also.put.the.low.limit.on.the.minimum.size.
of.plasmonic.nanomaterials.for.biosensing..The.nanosize.of.both.bioreceptors.and.nano-
structures. made. highly. miniaturized. signal. transducers. possible,. while. multiplex,. real-
time,.and.parallel.sensing.can.be.achieved.by.combining.the.highly.tunable.size,.shape,.
structures,.and.composition.of.plasmonic.nanostructures.with.a.wide.variety.of.available.
bioreceptors.and.rapid.development.of.surface.biofunctionalization.strategies.
This.synergetic.combination.of.plasmonic.nanostructures,.plasmonics,.and.surface.bio-
functionalization. offers. plasmonic. nanobiosensors. the. attractive. advantages. over. other.
biosensors. to. better. address. the. major. challenges. previously. mentioned. in. biosensing..
First.and.foremost,.plasmonic.nanobiosensors.have.tunable.optical.properties.to.it.a.wide.
variety.of.applications..The.frequency.and.intensity.of.the.nanoparticle.LSPR.extinction.
or.scattering.bands.are.highly.sensitive.to.size,.shape,.orientation,.composition,.and.struc-
ture. (e.g.,. shell-core. structure). of. the. NPs,. as. well. as. the. local. dielectric. environments,.
which. reduce. or. eliminate. ampliication. procedures.. Therefore,. the. LSPR. can. be. tuned.
during. fabrication. by. controlling. these. parameters. with. a. variety. of. chemical. synthesis.
and.nanofabrication.techniques..The.nanoparticle.array-based.biosensors.can.also.be.tran-
sitioned. to. single. NPs. to. improve. LSPR. sensitivity. to. the. level. of. a. single. molecule.. In.
addition,. plasmonic. nanobiosensors. possess. greater. spatial. resolution,. both. lateral. and.
normal,.compared.with.SPR..The.ultimate.lateral.spatial.resolution.is.achieved.with.single.
NPs..Plasmonic.nanobiosensors.have.an.inherent advantage of.the.label-free.nature.over.
other.optical.biosensors.that.require.organic.luorescent.dyes.or.inorganic.agents.such.as.
quantum.dots.to.transduce.the.binding.event.because the.measured.quantity.is.the.optical.
response.of.the.metal..The.label-free.nature.can.signiicantly.reduce.sample.preparation.
procedures.for.biosensing..Moreover,.unlike.luorophores,.plasmonic.NPs.do.not.blink.or.
bleach,. providing.a.virtually.unlimited.photon.budget.for.observing.molecular. binding.
over. arbitrarily. long. time. intervals,. which. makes. long-term. continuous. biosensing. pos-
sible..What's.more,.observation. of.local.surface.plasmons.can.be.done.using.simple.and.
inexpensive.spectrophotometric.equipment.in.the.transmission.(or.relection).conigura-
tion,.which.is.important.for.fabricating.a.large.biosensing.array.that.consists.of.thousands.
of.biosensors.
