Biomedical Engineering Reference
In-Depth Information
will.remain.an.impediment.to.its.usage.as.an.eficient.technique.
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.Physical.methods.that.
involve. direct. manipulation. of. the. cells. encompass. microinjection. and. electroporation..
High-voltage. electric. pulses. are. utilized. in. electroporation. (Figure 2.2B). to. temporarily.
increase.the.permeability.of.the.plasma.membrane.
76,96
.This.method,.similar.to.nonspeciic.
endocytosis,.is.suited.for.delivering.QDs.to.a.large.population.of.cells..The.direct.deliv-
ery.of.nanoparticles.into.the.cytoplasm.without.requiring.subsequent.endosomal.escape.
is. also. advantageous.. However,. intracellular. aggregation. of. the. electroporated. particles.
and.the.high.rate.of.cellular.death.due.to.the.applied.electrical.shock.are.major.problems.
with.this.technique.
94
.By.using.a.ine-tipped.glass.micropipette,.it.is.possible.to.directly
microinject
(Figure 2.2C). the. QDs. into. the. cytoplasm. of. individual. cells. in. a. monodis-
persed.form..In.spite.of.low.delivery.eficiency,.this.method.results.in.a.lower.rate.of.cel-
lular. death
74
. than. electroporation.. The. chemically. mediated. delivery. system. facilitates.
plasma.membrane.translocation.by.using.different.biomolecules,.including.cationic.pep-
tides.(Figure 2.2D).(e.g.,.HIV-derived.TAT.peptide),
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.various.proteins.(Figure 2.2E).(e.g.,.
transferrin),
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. small. molecules. (Figure 2.2F), such. as. nutrients. or. cofactors,
101
. or. over-
coating.with.amphiphilic.polymers.(Figure 2.2G).(e.g.,.phospholipid.micelles).
102
.For.high.
delivery.eficiency,.short.incubation.times,.minimal.toxicity,.a.relatively.small.size.of.the.
conjugated.particles,.and.an.ability.for.noncovalent.assembly.(i.e.,.biotin-avidin),.peptide-
mediated.delivery.appears.to.be.the.most.eficient.approach.for.delivering.nanoparticles.
into.the.living.cells;.however,.this.method,.like.others,.has.its.own.limitations.
103
.One.of.
the. main. issues. in. this. strategy. is. nanoparticles'. endosomal. entrapment,
23,50,104
. which. is.
not. an. impediment. in. applications,. such. as. whole. cellular. tracking. and. cytometery.
94
.
However,.targeting.and.imaging.of.particular.subcellular.components.such.as.cytoplas-
mic. proteins,. organelles,. and. complex. biomolecular. processes. in. living. cells
55
. requires.
access.of.the.bioconjugated.QDs.to.the.cytoplasm.or.nuclear.region..Using.microinjection.
of.QDs.conjugated.to.organelle-targeting.peptides,.Derfus.et.al..demonstrated.the.ability.
of.delivery.and.speciic.targeting.of.either.cellular.mitochondria.or.nuclei.in.ibroblasts.
94
.
Correspondingly,.electroporated.peptide-QD.conjugates.have.been.used.for.targeting.and.
imaging. of. the. nuclei. in. living. cells.
105
. Antibody-conjugated. QDs. encapsulated. within. a.
biodegradable. nanocomposite. have. been. designed. by. Kim. et. al.
106
. for. facilitating. multi-
plexed. labeling. of. subcellular. structures. inside. living. cells.. This. bioresponsive. delivery.
system,. which. undergoes. endolysosomal-to-cytosolic. translocation,. enables. controllable.
release.of.the.functionalized.QDs.through.hydrolysis.of.the.polymeric.capsule.within.the.
cytoplasmic.compartment..Noninvasive.monitoring.of.multiple.organelles,.structures,.and.
intracellular. processes. by. using. QDs. can. open. up. the. probability. of. studying. different.
molecular.interactions.and.complex.biological.processes.inside.living.cells.
2.7 InVivoApplicationofQuantumDots
The. superior. photophysical. aspects. of. QDs,. together. with. the. signiicant. improvement.
in.their.synthesis,.coating,.and.conjugation.techniques,.have.made.QDs.the.luorophores.
of. choice. in. wide-ranging. cellular. and. molecular. imaging. applications,
55
. based. on. their.
use.as.luorescent.labels.or.contrast.agents.
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.The.ability.of.real-time.tracking.of.single-
cell. migration. and. differentiation. is. assumed. to. be. important. in. a. number. of. research.
areas,.such.as.embryogenesis,.cancer.metastasis,.and.stem.cell.therapeutics.
59
.In.addition,.
