Biomedical Engineering Reference
In-Depth Information
the.two.types.of.cells.were.transported.in.opposite.directions.when.the.dominant.signals.
were.running.at.a.desired.frequency.and/or.amplitude.(Pethig.et.al..2003).
17.4.7 DeP Manipulation by OeT
With.easy.coniguration.of.virtual.electrodes.from.optical.imaging,.OET.has.been.dem-
onstrated. for. trapping,. rearrangement,. and. sorting. various. colloids,. including. polysty-
rene.particles.(Chiou.et.al..2005;.Ohta.et.al..2007b),.semiconductive.or.metallic.nanowires.
(Jamshidi.et.al..2008),.bacteria.(Chiou.et.al..2004),.and.a.variety.of.mammalian.cells.(Lu.
et.al..2005;.Ohta.et.al..2007a,b;.Hwang.et.al..2008;.Neale.et.al..2009)..Some.lab-on-chip.plat-
forms,. such. as. particle. counters. and. microluidic. low. cytometry,. have. been. developed.
and.OET.was.widely.integrated.to.focus,.delect,.and.separate.particle.samples.(Lin.and.
Lee.2008)..It.is.nowadays.considered.a.potential.alternative.in.some.DEP.and.optical.twee-
zers.applications.
17.5 Concluding Remarks and Perspectives
In.an.inhomogeneous.electric.ield,.the.DEP.force.drives.microscale.or.nanoscale.particles.
to. move. along. or. against. the. electric. ield. gradient,. depending. on. their. polarization. in.
the.luid.medium..With.appropriate.electrode.designs,.DEP.has.been.successfully.applied.
to. trap,. transport,. concentrate,. and. separate. various. latex. beads,. DNA,. cells,. and. other.
colloids.. Just. like. the. development. of. many. new. technologies,. progress. in. DEP. greatly.
beneits. from. the. emergence. of. microelectromechanical. systems. (MEMS). technologies.
and.the.recent.high. demand.for.eficient. tools.in.life.science.. The.former.helps.improve.
the. construction. of. DEP. electrodes. from. simple,. large. electric. wires. to. well-patterned.
sophisticated.micropads.or.virtual.electrodes.and.greatly.broadens.the.trapping.capability.
and. the. separation. resolution. of. DEP.. The. latter. stimulates. research. interests. in. the.
exploration. of. valuable. application. potentials. of. DEP. systems.. With. their. help,. DEP. has.
gained.signiicant.advances.in.both.theory.and.technology.in.the.past.two.decades,.which.
are.endorsed.by.the.large.number.of.DEP-related.patents.and.publications.released.every.
year..However,.DEP.technology.has.not.yet.been.completely.promoted.from.researchers'.
lab.to.the.technology.market..Its.commercialization.is.still.facing.some.bottlenecks.after.a.
half-century.of.development.
The. irst. issue. comes. from. its. slow. speed.. Unlike. optical. tweezers,. DEP. force. aims. at.
the.manipulation.of.a.large.population.of.objects..But.its.current.throughput.or.capacity.
is. relatively. small. (e.g.,. 100.μL/h). and. cannot. satisfy. the. criteria. of. many. separation.
applications.. Although. it. has. been. much. improved. with. the. introduction. of. DEP-FFF.
and. TWD,. more. eficient. separation. including. the. improvement. on. its. separation. speed.
and.resolution.will.surely.accelerate.its.maturation..The.second.issue.is.associated.with.
several. negative. impacts. for. its. use. of. the. high. electric. ield. and. ield. gradient,. such. as.
the. electrohydrodynamic. instability. and. Joule. heating.. With. new. electrode. design. and.
fabrication,.these.effects.could.be.avoided.or.largely.suppressed..In.fact,.some.efforts.(e.g.,.
the.use.of.EDEP).have.been.incorporated.recently.toward.the.removal.of.these.barriers..
The.third.challenge.comes.from.the.electrode.fabrication..This.issue.has.also.been.largely.
tackled.with.MEMS.technologies..For.examples,.CMOS-like.electrode.design.avoids.the.
fabrication.dificulties.in.multiple-layer.DEP.electrodes.and.further.enables.the.potentials.
