Biomedical Engineering Reference
In-Depth Information
nanopore,
l
m
< H
eff
, the measured current blockage amplitude
DI
b
is expected to be
directly proportional to the excluded volume
of a protein molecule as described in
Eq. (6.1). In addition, when a native state protein molecule is passing through a
nanopore driven by an electric field, the time duration
t
d
is expected inversely
proportional to its electrical charge
Q
as described in Eq. (6.3). In this section,
based on our experimental results and data analysis, we discuss the resolution of
using ion beam sculpted silicon nitride nanopores on measuring a protein's size and
relative electrical charge.
L
6.4.1 Sizing Protein Molecules
Figure
6.3
demonstrates the use of a solid-state nanopore to measure and discriminate
the size of native state proteins. Using a 22 nm nominal diameter pore, three different
proteins were measured sequentially: BSA (66.4 kDa, 607 aa,
18
e
), Fibrinogen
(340 kDa, ~1,500 aa,
16
e
), and Laminin M (850 kDa, ~3,110 aa, +34
e
). Event
density plots in Fig.
6.3a, b, c
show that the current blockage amplitude was
correlated to protein size (Fig.
6.3d
):
DI
b
(Laminin)
¼
84 pA
> DI
b
(Fibrinogen)
¼
74 pA
> DI
b
(BSA)
¼
50 pA. Figure
6.3e
shows that the time duration followed the
same trend:
s. Laminin has
twice the electrical charge than BSA and Fib but its
t
d
is the longest, which suggests
that the time
t
d
depends on both the electrical charge and molecular size,
t
d
~
t
d
(Lam)
¼
154
m
s
> t
d
(Fib)
¼
101
m
s
> t
d
(BSA)
¼
64
m
L
/Q,
Fig. 6.3 Event Number density plots for BSA (a), Fibrinogen (b), and Laminin (c) in 1 M KCl,
40% Glycerol, pH
¼
7. The current drop (d), time duration (e), and the integrated area of events for
all three proteins (f). The pore used was 22
2 nm made by Ar at 3 kV. The low pass filter was set
at 100 kHz for this set of data
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