Biomedical Engineering Reference
In-Depth Information
Outlet 2
Deflection
electrode
F
nDEP
Outlet 1
Inlet
Cell
F
stokes
α
Small particle
Large particle
(a)
(b)
100 μm
100 μm
(c)
(d)
Figure 17.10
(See companion CD for color igure.)
.DEP.levitation.for.particle.delection..(a).Schematic.diagram.of.the.DEP.
levitation.with.both.a.delector.electrode.and.involved.physical.forces.illustrated,.(b).particles.were.delected.for.
separation,.and.(c.and.d).OET.delection.to.separate.particles.of.two.different.sizes.9.7.and.20.9.μm..(Reproduced.
from.
Biosens. Bioelectron.,
.24,.Lin,.Y..and.Lee,.G.,.Optically.induced.low.cytometry.for.continuous.microparticle.
counting.and.sorting,.572-578,.Copyright.2008,.with.permission.from.Elsevier.)
Alternatively,.EDEP.and.OET.can.also.be.used.as.delectors.(Figure.17.10b)..With.the.same.
delecting.mechanism,.virtual.electrodes.instead.of.metallic.electrodes.were.used.in.OET.at.
appropriate.locations.through.illuminating.the.photoconductive.layer.(Lin.and.Lee.2008)..
An.EDEP.delector.has.insulator.post.arrays.in.the.low.channel..The.bended.electric.ield.
around.the.insulator.posts.creates.zones.of.high.and.low.ield.strengths.at.different.locations.
to.redirect.particles.from.their.original.paths.to.attain.the.delection.(Cummings.et.al..2000).
17.4.4 DeP Levitation for Particle Concentration and Focusing
In.EDEP,.the.constriction.structures.are.natural.locations.for.particle.trapping.with.its.high.
ield.gradient.feature..As.shown.in.Figure.17.11a,.with.a.constriction.opening.of.0.5-1.0.μm,.
targeted.objects.from.DNA.of.1.kbp.to.
E. coli
.cells.were.trapped.with.an.applied.ield.of.
200-300.V/cm.at.a.frequency.of.1-2.kHz..When.a.low.continuously.brings.particles.to.the.
trapping.sites.(the.constriction),.they.are.quickly.concentrated.or.enriched.there..Studies.
showed.that.DNA.trapping.occurred.at.a.frequency.much.lower.than.those.needed.with.
metallic.electrodes.and.the.concentration.eficiency.increased.when.raising.the.signal.fre-
quency.between.200.Hz.and1.kHz.(Chou.et.al..2002)..A.similar.particle.focusing.effect.was.
also. demonstrated. with. the. insulator. post. array. based. EDEP. systems. (Cummings. et. al..
2000)..Such.simple.concentration.phenomenon.is.very.useful.if.quick.concentration.of.par-
ticles.from.a.diluted.suspension.is.necessary..For.example,.in.DNA.hybridization.or.patho-
gen.identiication.assays,.the.initial.samples.only.have.trace.amounts.of.materials.beyond.
the.detecting.limit..Concentration.of.these.samples.is.required.prior.to.further.analysis.and.
EDEP.has.often.been.integrated.in.lab-on-chip.devices.for.this.purpose.(Chou.et.al..2002).
