Biomedical Engineering Reference
In-Depth Information
approval..For.many.nanoparticles,.off-label.uses.are.popular.within.the.wider.biomedical.
community.
In.this.chapter,.we.will.irst.discuss.current.cell.tracking.agents,.and.then.describe.in.
detail.the.unique.role.of.nanoparticles.in.biomedical.imaging,.the.physicochemical.struc-
ture.and.applications.of.quantum.dots.and.superparamagnetic.particles,.and.their.appli-
cations.in.biomedical.imaging.research.
2.2 CellTrackingAgents
Biomedical. imaging. involves. the. techniques. and. process. used. to. create. images. of. bio-
logical.material.(or.parts.and.function).for.research. or.clinical.purposes..Although.usu-
ally.light,.photonic.waves.are.used.to.make.cells.or.tissue.visible,.in.biomedical.imaging.
this.process.can.be.done.by.other.kinds.of.waves,.such.as.x-ray.or.magnetic.ield,.and.all.
of. them. are. a. type. of. energy.. Thus,. imaging. needs. an. energy. source,. detectable. waves,.
and. detectors.. Contrast. or. staining. agents. are. substances. used. to. enhance. the. visibility.
of. target. structures. by. increasing. the. energy. relection. from. the. targets.. Suitable. agents.
for.labeling.the.cellular.property.of.interest.are.crucial,.and.a.lack.of.these.agents.often.
limits. study. results.. Long-term. biological. compatibility,. safety,. brightness,. stability,. and.
the.possibility.to.distinguish.several.markers.simultaneously.are.the.major.requirements.
for.these.agents.
It.is.relatively.easy.to.create.a.wish.list.of.the.properties.describing.an.ideal.cell.stain-
ing. and. tracking. agent.. However,. there. is. no. single. agent. that. allows. a. comprehensive.
approach. to. stem. cell. imaging,. as. stem. cell. development. involves. a. heterogeneous. and.
interactive.cast.of.players.that.evolves.over.time..Thus,.it.is.logical.to.have.a.spectrum.of.
agents.from.low.to.high.resolution.to.label.a.wide.variety.of.cell.types.with.sensitive.and.
quantitative. multiparameter. properties. for. monitoring. how. a. selected. subpopulation. of.
cells.would.subsequently.expand.or.evolve..At.one.end.of.this.spectrum,.positron.emis-
sion.tomography,.magnetic.resonance.imaging.(MRI),.and.optical.coherence.tomography.
provide.real-time.readouts.from.animal.or.human.subjects,.with.resolutions.of.approxi-
mately.~1,.~100,.and.~10.µm,.respectively..At.the.other.end,.electron.microscopy.provides.
near-molecular-level.spatial.resolution;.however,.the.cell.must.be.ixed,.which.is.invasive.
and. prevents. dynamic. imaging.. Fluorescence. modalities. provide. a. range. of. spatial. and.
temporal.resolution.between.these.two.resolution.extremes,.but.it.is.not.enough.to.have.
suitable.resolution.for.in.vivo.imaging..Nanoparticle-based.contrast.agents.extended.this.
range.to.have.appreciable.resolution.for.cell.imaging..However,.to.precisely.depict.the.role.
of.nanoparticles.in.biological.imaging,.properties.of.commonly.used.imaging.modalities.
should.irst.be.clariied..As.the.irst.step,.the.advantages.and.disadvantages.of.common.
conventional.contrast.agents.will.be.discussed,.and.then.the.quantum.dots.and.superpara-
magnetic.particles.used.as.nanoparticles.will.be.described.in.detail.
The.most.important.imaging.modalities.for.live.cell.tracking.at.single-cell.resolution.use.
luorescence.or.MRI..Radio-nucleated.magnetic.resonance.and.luorescent.probes.are.the.
main.contrast.agents.used.in.medical.imaging.
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.Radiolabels,.as.the.oldest.contrast.agents,.
such. as. 51Cr,. 125I,. or. 111In,. are. sensitive. detectors. for. very. small. numbers. of. cells,. and.
labeling. procedures. are. relatively. simple.. These. labels. have. traditionally. been. used. for.
tagging.targets.used.in.cell-mediated.cytotoxicity.assays,.in.vivo.biodistribution.studies,.
