Biomedical Engineering Reference
In-Depth Information
Fig. 7.20
Schematic diagram
showing nanofluidic channels
with or without steep entropy
barrier. (
a
) When long DNA
molecules are drawn by
hydrodynamic flow or electric
field from a high-entropy area
to confining nanochannels,
the molecules tend to stick at
the entrances of the channels
due to the steep entropy
barrier shown on the curve.
(
b
) Micro-post array and an
interfacing region of fluidic
structures with gradient
dimensions designed to
pre-stretch DNA molecules
before entering nanochannels,
resulting in a gradually
reduced entropy and less
steep barrier curve (Reprinted
with permission from Ref.
[
90
]. Copyright 2002,
American Institute of
Physics)
colors and sophisticated super-resolution techniques to increase the number of
resolved distances between individual DNA molecules. Improving resolution would
have advantages for detecting even smaller structural variations and increasing the
information density of the output.
Funnel-shaped microchannels can produce elongational flow, and this type
of fluidic flow was proved to be conducive to DNA elongation by Larson and
coworkers [
93
]. Elongational flow in the microfluidic funnel combines with shear
flow that can cause the DNA to tumble, and the two influences compete and
demonstrated that increased accumulated fluid strain and increased strain rate pro-
duced higher stretching efficiencies, despite the complications of shear interactions.
They discussed the influence of the strain rate on DNA stretching by fabricating
differently tapered microfluidic funnels (Fig.
7.21
) and found the optimal geometry
of microchannel for DNA stretching. The same group reported similar tapered
microfluidic channels, but with a pillar array immediately preceding the stretching
funnel [
94
]. They speculated that pillars may be unnecessary although smaller and
more tightly packed pillars may be functional for DNA stretching. Microfluidic
design conducted an effective and simple DNA stretching.
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