Biomedical Engineering Reference
In-Depth Information
Figure 8
. Numerical simulation of dimensionless binding curves for non-enhanced (0 V) and
enhanced (7 V, 14 V) transport. The differences in the two curves show an increase in binding
rate, which yields a factor of 4 higher binding for 7 V and a factor of 8 higher binding after 30
seconds for 14-V applied root-mean square potential. The binding improvement for the 14-V
case decreases to around sixfold after 100 seconds: the binding is no longer completely trans-
port-limited.
rate of change of antigen bound to the immobilized antibodies is equal to the
rate of association minus the rate of dissociation:
s
B
=
kC R
(
B
)
k B
.
[17]
a
T
d
s
The rate of antigen binding to immobilized antigen, 0
B
/0
t
, must be balanced by
the diffusive flux of antigen at the binding surface,
y
= 0, such that
s
B
s
C
=
D
.
[18]
s
t
s
y
y
=
0
Equations [16]-[18] are solved with an initial antigen concentration
C
0
= 1 nM
and an immobilized antibody concentration
R
T
= 1.7 nM cm (i.e., one molecule
per 100 nm
2
). The binding rates for three conditions, 0-, 7-, and 14-V root-mean-
square voltage, are shown in Figure 8. The 0-V case corresponds to the passive
case, which is the result of pure diffusion. This is the standard mode of most
immobilized assays, such as ELISA. The 7- and 14-V curves correspond to the
result of electrothermally driven flow enhancing transport of antigen to the im-
mobilized antibodies. The curves in Figure 8 show that a factor of up to 8
(800%) improvement in sensitivity (or response) is obtained by using AC elec-
trokinetics.
