Biomedical Engineering Reference
In-Depth Information
high-throughput single-cell analysis becomes feasible. heir device consisted of a simple lin-
ear channel (in which the cells are loaded) with one narrow side branch (through which the
chemoattractant α-methylaspartate and luorescein as a tracer are loaded through a valve). he
low in the large cell-containing channel did not signiicantly penetrate the chemoattractant-
containing channel, but created a transient gradient to which cells responded. Strong chemotaxis
is visible in
Figure 6.36g
, where most cells swim up the gradient (high chemotactic velocity
V
C
),
but not in
Figure 6.36h
(low
V
C
), likely due to receptor saturation. his type of microluidically
generated ephemeral gradients provide realistic microenvironmental signals that mimic the
signals encountered by bacteria in their natural habitats and their responses to nutrient pulses.
Mingming Wu's group at Cornell University was able to fully suppress low using a three-
channel gradient generator in which the luids are separated by semiporous agarose barriers
(conceptually similar to Manson's device, in which the barriers were made of paper) by building
the device in agarose (
Figure 6.37
). he bacteria were introduced in the central channel whereas
the lanking channels served as sink and source to create a stable gradient without exposing the
cells to low (all channels are 400 μm wide and 160 μm deep). Single-cell chemotactic trajectories
could be tracked for various concentration values of methyl-aspartate (the ligand used in this
study). Both the ligand concentration ([
L
]) proile (as visualized by adding luorescein) and the
(a)
(b)
(c)
Flow
x
= 0
x
= 6 mm
x
M
(d)
200 µm
x
= 0
x
= 6 mm
0.6
Microcapillary
Passive
valve
(e)
(f )
0.4
0.2
100 µm
1200
1400
1600
1800
x (µm)
(g)
(h)
C
= 0.06 mM,
dC
/
dx
= 0.08 mM/mm
V
c
= 12.6 µm s
-1
, β = 0.46
C
= 0.29 mM,
dC
/
dx
= 0.15 mM/mm
V
c
= 2.7 µm s
-1
, β = 0.78
FIGURE 6.36
Tracking. of. single. bacterial. cells. in. low-free. microluidic. chemotactic. gradients..
(From.Tanvir.Ahmed.and.Roman.Stocker,.“Experimental.veriication.of.the.behavioral.foundation.of.
bacterial.transport.parameters.using.microluidics,”.
Biophys. J.
.95,.4481-4493,.2008..Reprinted.
with.permission.from.Elsevier..Figure.contributed.by.Roman.Stocker.)
