Bionanotechnology Strategies for Cell Detection - Bionanotechnology: Global Prospects - page 21

The.intense.brightness.of.QDs,.as.well.as.their.exceptional.photostability,.enables.real-
time.tracking.of.a.single.particle.over.an.extended.period.of.time,.which.is.a.potent.approach.
to.study.the.molecular.behavior.underlying.biological.events.such.as.cell.membrane.orga-
nization,.lateral.diffusion.of.molecules,.and.molecular.interactions. 89-91 .Through.the.use.
of. streptavidin-functionalized. CdSe-ZnS. QDs,. individual. glycine. receptors. have. been.
monitored.in.the.synaptic.cleft.of.live.spinal.neurons.for.durations.longer.than.20.min. 63 .
Antibody-conjugated.QDs.have.been.used.for.the.visualization.of.integrin.dynamics.dur-
ing.osteogenic.differentiation.of.human.bone.marrow-derived.progenitor.cells.(BMPCs). 92 .
Lidke.et.al..used.the.epidermal.growth.factor.(EGF)-conjugated.QD.to.directly.image.the.
internalization.of.EGF.receptors.and.the.subsequent.signaling.pathways. 93
Two. distinct. methods. are. followed. in. intracellular. labeling:. irst,. whole. cell. labeling,.
which.is.particularly.of.interest.when.a.speciic.cell.population.is.aimed.to.be.detected.or.
tracked,.as.in.cell.lineage.studies, 28 .and.second,.when.particular.subcellular.compartments.
inside. a. living. cell. are. desired. to. be. targeted. and. tracked,. which. represents. a. powerful.
tool. in. molecular. cell. biology. 94 . In. contrast. to. cell. membrane. targeting,. the. intracellular.
delivery.of.QDs.in.living.cells.is.confronted.with.some.dificulties..A.major.problem.is.the.
lack.of.an.eficient.method.to.transport.QDs.across.the.plasma.membrane.barrier.without.
disturbing.the.cell.membrane.and,.in.the.case.of.intracellular.speciic.targeting,.preven-
tion.of.entrapment.in.the.endocytic.pathway.or.aggregation.in.the.cytoplasm.
Intracellular. delivery. of. nanoparticles. in. living. cells. can. be. achieved. by. both. physi-
cal.and.biochemical.strategies.(Figure 2.2),.except.nonspeciic.endocytosis.(Figure 2.2A),.
which. depends. on. the. electrostatic. interaction. among. nanoparticles. and. cellular. mem-
brane,.as.well.as.the.innate.capacity.of.most.cells.to.uptake.nanoparticles.from.extracellu-
lar.space.via.endocytosis.in.a.size-.and.charge-dependent.manner. 50,95 .The.main.advantage.
of.this.passive.delivery.is.its.simplicity.and.the.ability.to.deliver.QDs.to.a.large.number.
of.cells.simultaneously..However,.endosomal.escaping.and.the.potential.for.cytotoxicity.
FIGURE 2.2
Intracellular.delivery.of.QDs.by.using.different.strategies..A).non-speciic.endocytosis,.B).electroporation,.C).
microinjection,.D).peptide-mediated.uptake,.E).protein-mediated.delivery,.F).small.molecules,.and.G).polymer-.
mediated.delivery..