Biomedical Engineering Reference
In-Depth Information
Fig. 1.8 Dwell time histograms for the transport of 5 kbp dsDNA through a 7 nm nanocrystalline
Al
2
O
3
nanopore in 100 mM KCl, 10 mM Tris, pH 7.5 buffer at applied voltages of (a) 100 mV
(b) 300 mV and (c) 500 mV [
90
], reprinted with permission. Each distribution is fitted with a
bi-exponential function (
black line
) with two time constants, t
1
and t
2
, indicating two distinct types
of polymer transport, fast translocation governed by polymer hydrodynamics and slow transloca-
tion regulated by polymer-pore interactions. (Insets) Blockage Ratio (B
r
) vs. Dwell time (t
D
) [ms]
event density plots at each voltage. Grayscale bar represents number of events. At higher voltages,
a greater percentage of events exhibit fast translocation dynamics bounded by the arrows in
the insets. Translocation events exhibit clear voltage dependence (d) Summary of results from
the electrical sensing of 5 kbp dsDNA through 7 nm Al
2
O
3
nanopores.
t
D
Dwell time (time
biomolecule resides in the pore);
t
1
Time constant corresponding to fast translocation;
t
2
Time
constant corresponding to slow translocation;
B
r
Blockage Ratio (percentage of open pore
current that is blocked during DNA translocation);
n
Biomolecule Flux (total number of events
during 5 min of recording);
R
Capture Rate (average number of translocation events per second)
negatively charged surface at pH 7.5 resulting from the deprotonation of surface
silanol groups [
35
]. Furthermore, a comparison of the surface charge density of
Si
3
N
4
and
g
-Al
2
O
3
surfaces at pH 7.5 (in monovalent salt solution at concentration
10
4
M) revealed a charge density that is approximately six times higher in
1
-Al
2
O
3
(50 mC/m
2
) than in Si
3
N
4
(8 mC/m
2
) systems [
1
,
81
]. Thus, polymer-pore
interactions involving electrostatic binding events are expected to be more pro-
nounced in Al
2
O
3
nanopores.
The importance of polymer-pore interactions are explored further in the follow-
ing section through nanopore based chemical modification. Chemical modification
and surface functionalization of nanopores has helped usher in the next generation
of nanopore sensors relying on polymer-pore interactions to achieve selective and
facilitated transport of various biomolecules through individual nanopores and
nanopore arrays.
g
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