Biomedical Engineering Reference
In-Depth Information
Detection point
(nanopillar-free region)
E
2
180 μm
35 μm
35 μm
E
1
E
3
380 μm
500 μm
500 μm
25 μm
500 nm
500 nm
E
4
2700 nm
(a)
0 s
0 s
2 s
2 s
4 s
4 s
6 s
6 s
8 s
8 s
10 s
10 s
(b)
< λ DNA >
20 μm
< T4 DNA >
20 μm
Figure 18.3
(a).Schematics.of.artiicial.EP.using.nanopillar.array;.(b).Collision.of.a.single.λ-DNA.(left).and.T4-DNA.(right).
with.nanopillar.arrays..(Reproduced.with.permission.from.Kaji,.N.,.Tezuka,.Y..Takamura,.Y..et.al.,.
Anal. Chem
.,.
76,.15-22..Copyright.2004.American.Chemical.Society.)
found.to.affect.the.eficiency.of.long.DNA.separation..It.has.also.been.demonstrated.that.
artiicial.nanopillar.arrays.are.superior.to.conventional.gel.EP.in.separating.large.DNAs..
However,. nanopillar. arrays. still. cannot. separate. short. DNA. molecules. (<10.kbps). and.
do.not.show.better.separation.than.capillary.EP..This.is.because.the.size.and.spacing.of.
nanopillar.arrays.are.still.large.compared.to.the.entangled.polymer.matrix.in.capillary.EP..
It.is.possible.to.use.smaller.and.denser.nanopillar.arrays.to.achieve.better.DNA.separation,.
but.more.sophisticated.fabrication.techniques.are.needed.and.the.cost.also.increases.
Entropy.trapping.has.been.used.to.separate.DNA.molecules..This.method.uses.nano-
channels.with.alternating.depths..The.deep.channel.has.a.size.comparable.to.the.gyration.
radius.of.DNA.molecules.(around.several.microns),.while.the.depth.of.the.shallow.channel.
is.<100.nm..It.is.shown.that.larger.T2-DNA.molecules.move.faster.in.the.entropic.trapping.
array.than.smaller.T7-DNAs.(Han.et.al..1999;.Han.and.Craighead.2000)..This.is.because.
the.gyration.radius.of.a.T7-DNA.is.smaller.than.the.size.of.the.trap.(i.e.,.deep.channel).and.
it.is.more.likely.to.stay.in.the.trap.where.the.electric.ield.is.much.weaker.than.that.near.
the.entrance.of.the.shallow.channel..Thus,.smaller.DNA.has.dificulty.in.gaining.enough.
