Biomedical Engineering Reference
In-Depth Information
Using (
9.1
), or variations of it, Staufer's group and others estimated the volume
of different proteins [
13
,
15
,
16
,
38
,
46
]. One of the first successful experiments to
detect single proteins identified unlabeled bovine serum albumin (BSA). In this
work, Han et al. used an adaptation of (
9.1
)
1
to estimate the size of BSA and found it
had a diameter of 7-9 nm [
16
]. In another study, Fologea et al
.
compared BSA with
the similarly charged but larger protein fibrinogen. Here the authors could readily
distinguish these proteins because larger peak amplitudes and translocation times
were measured with fibrinogen than BSA as expected from (
9.1
)[
13
].
A more recent investigation by Han et al
.
distinguished between four proteins,
ovalbumin (OA), avidin (AV), BSA, and streptavidin (SA), using a pore with a
diameter of 28 nm based on values of
DI
[
15
]. Figure
9.2a
shows a histogram of the
distribution of
DI
for each of these proteins.
Moreover, the linear relationship between
(
t
) can be used to identify
the size of protein complexes and the binding of proteins to viruses or particles that
display ligands. Saleh and Sohn used pores with a diameter of 1
DI
(
t
) and
L
m
m to detect
Fig. 9.2 (a)Histogram
showing
DI
counts for the
proteins BSA (white), OA
(black), and SA (grey) at pH 6.
(b) Translocation time of
different proteins as a function
of pH in the recording
electrolyte (
filled square
:OA;
filled circle
:BSA;
filled
triangle
: SA; and
open circle
:
AV). The range of pH values
used was selected such that
proteins were soluble and no
visible aggregates formed in
order to avoid clogging.
Adopted from Han et al
.
with
permission [
15
]
1
This adapted equation normalized
DI
with respect to the baseline current of translocation
events,
I
. With this equation, the diameter of the molecules,
d
m
, could be determined:
d
m
3
¼
ðl
p
þ
0
:
8
d
p
Þd
p
2
, with
s
1.
s
DI
I
Search WWH ::
Custom Search