Biomedical Engineering Reference
In-Depth Information
50 μm
Flow
Ex:I,II
Ex:III
Z
20 μm
5 μm
Figure 18.4
(See companion CD for color igure.)
.Schematics.of.the.DLA.technology.for.DNA.mapping..(Reproduced.with.
permission.from.Chan,.E.Y..et.al.,.
Genome Res
.,.14,.1137..Copyright.2004,.Cold.Spring.Harbor.Laboratory.Press.)
18.4.3 Nanofluidic gene Delivery
Gene. delivery. is. the. process. of. introducing. foreign. DNAs. into. host. cells.. One. of. the.
most. interesting. nonviral. gene. delivery. methods. is. electroporation,. which. temporarily.
breaks.down.the.cell.membrane.using.the.pulsed.electric.ield..Cell.membrane.has.a.lipid-
bilayered.structure.with.a.thickness.of.5-10.nm.and.is.almost.nonconductive..When.a.cell.
is.placed.in.an.electric.ield,.there.is.a.potential.difference.across.the.cell.membrane..This.is.
called.the.transmembrane.potential..The.critical.transmembrane.potential.to.break.down.
the.cell.membrane.is.typically.around.1.V..Considering.the.thickness.of.cell.membrane,.the.
electric.ield.across.the.thin.cell.membrane.is.huge.(∼10
8
.V/m),.and.thus,.cell.membrane.can.
be.easily.broken.down.
Compared. with. the. bulk. electroporation. (BEP),. which. uses. relative. high. voltage. drop.
and.causes.a.predominant.amount.of.cell.deaths,.recent.research.on.luidic.electroporation.
mainly.focuses.on.using.microluidic.devices.to.facilitate.controlled.electroporation.and.
to. minimize. cell. death.. These. efforts. include. membrane. sandwich. electroporation. (Fei.
et.al..2007,.2010).and.continuous.or.semicontinuous.low.electroporation.(Wang.et.al..2009;.
Zhan.et.al..2009)..Fundamental.investigation.of.single-cell.response.in.microelectroporation.
(MEP).has.also.been.carried.out.by.observing.how.luorescent.dyes.enter.the.cell.through.
the. temporarily. opened. membrane.. A. single. cell. is. either. suspended. and. placed. on. the.
surface.(Golzio.et.al..2002),.trapped.in.a.microchannel.(Khine.et.al..2005),.or.immobilized.
by.optical.tweezers.(Henslee.et.al..2011).
However,. most. research. is. focused. on. the. design. of. MEP. devices.. Few. realized. that.
the. distribution. of. transmembrane. potential. on. cell. surfaces. is. the. key. to. measure. the.
eficiency. of. electroporation. and,. thus,. can. be. used. as. a. standard. to. evaluate. different.
electroporation. devices.. Finite. element. simulation. has. been. used. to. calculate. the.
transmembrane.potential.for.MEP.(Zudans.et.al..2007;.Fei.et.al..2010)..Through.calculation.
of.transmembrane.potential,.we.know.the.reason.why.MEP.is.better.than.the.BEP..This.is.
because.MEP.creates.a.higher.and.more.focused.transmembrane.potential.distribution.on.
the.cell.surface..Thus,.a.smaller.area.of.cell.membrane.is.temporary.broken.down..However,.