Biomedical Engineering Reference
In-Depth Information
ITO-coated.conductive.glass.plate.electrodes,.and.one.of.them.is.further.coated.with.a.thin.
layer. of. amorphous. silicon. (∼1.μm. in. thickness),. as. shown. in. Figure. 17.7a.. The. electrical.
impedance.of.this.silicon.layer.is.photosensitive:.its.value.is.higher.than.the.illed.liquid.
medium.between.the.two.electrode.plates.when.in.dark,.while.several.orders.lower.than.
the. liquid. when. illuminated.. Therefore,. upon. applying. an. AC. signal. and. selectively.
exposing.the.Si-coated.surface,.the.voltage.drop.between.the.two.electrodes.varies:.in.an.
illuminated.area,.the.majority.voltage.drop.occurs.in.the.liquid.while.in.an.opaque.area,.it.
switches.to.the.coated.Si.layer.on.the.electrode.plate..This.results.in.a.nonuniform.electric.
ield.in.the.liquid.medium.and.the.generation.of.a.DEP.force.on.the.suspended.particles.
(Figure. 17.7a. and. b).. In. OET,. the. selective. exposure. is. attained. by. focusing. a. prescribed.
optical. image. from. the. digital. micromirror. display. (DMD). onto. the. Si-coated. ITO. glass.
plate.. The. generated. virtual. electrodes. can. be. conveniently. reconigured,. if. necessary,.
to.meet.the.needs.of.multiple.DEP.actuations,.such.as.trapping,.reposition,.and.sorting,.
similar.to.those.done.with.holographic.optical.tweezers.(Figure.17.7c.through.f)..But.unlike.
in. optical. tweezers. where. highly. focused. laser. beams. are. required,. OET. can. provide.
effective. particle.regulations. with.various. light.sources,. from. low. power. laser.beams.to.
cheap.LED.and.halogen.lamp.(Hwang.et.al..2008).
17.4 DEP Applications
In. DEP,. particles. move. along. or. against. the. electric. ield. gradient. and. gradually. aggre-
gate.at.desired.locations..Such.particle.trapping.is.determined.by.the.ield.strength.and.
the.angular.frequency.of.the.applied.electric.signal,.the.dimensions.of.the.particles,.and.
the.dielectric.properties.of.the.particles.and.their.surrounding.medium..With.appropriate.
electrode.designs,.the.DEP.force.on.the.particles.of.a.mixture.can.be.signiicantly.different,.
leading.to.their.concentration.at.different.locations.and.even.separation..In.the.past.two.
decades,.DEP-based.particle.separation.and.sorting.have.been.successfully.demonstrated.
with. latex. beads. (Muller. et. al.. 1995,. 1996b;. Green. and. Morgan. 1997,. 1998,. 1999;. Hughes.
and. Morgan. 1999;. Hughes. et. al.. 1999;. Hughes. 2002a),. DNA. (Washizu. and. Kurosawa.
1990;.Washizu.et.al..1995;.Porath.et.al..2000;.Tsukahara.et.al..2001;.Chou.et.al..2002),.cells.
(Marszalek.et.al..1989;.Masuda.et.al..1989;.Washizu.et.al..1990;.Huang.et.al..1992;.Pethig.
et.al..1992;.Wang.et.al..1993;.Becker.et.al..1994;.Markx.et.al..1994a,b,.1996;.Becker.et.al..1995;.
Stephen. et. al.. 1996),. and. other. biological. or. nonbiological. colloids. (Washizu. et. al.. 1994;.
Bezryadin.et.al..1997;.Bubke.et.al..1997;.Yamamoto.et.al..1998;.Smith.et.al..2000;.Chen.et.al..
2001;.Duan.et.al..2001;.Hermanson.et.al..2001)..Besides.particle.separation,.nontraditional.
DEP. actuation. technologies,. such. as. delection,. focusing,. transportation,. and. assembly,.
were.also.widely.explored.(Muller.et.al..1999;.Zheng.et.al..2004;.Lin.and.Lee.2008)..They.
greatly.broadened.the.applications.scheme.of.DEP,.from.purely.particle.trapping.to.par-
ticle.manipulation,.nanostructure.fabrication,.and.various.applications.in.life.science.
17.4.1 DeP Trapping for High-Throughput Separation
DEP-based.separation.is.usually.attained.in.luid.lows..The.major.role.that.conventional.
DEP. systems. play. for. separation. is. to. attract. wanted. particles. toward. the. ield. minima.
(n-DEP).or.maximum.(p-DEP).and.to.hold.them.there..The.low.takes.other.particles.expe-
riencing.weak.or.no.DEP.forces.away.continuously.(maybe.collected.as.well)..The.trapped.
