Biomedical Engineering Reference
In-Depth Information
The binding of
E.
coli to both the immunosensor with PAPG (
Abu-Rabesh et al., 2009
),
and to the antibody-conjugated magnetic beads (
Lee et al., 2009
) is described by a sin-
gle-fractal analysis. This indicates that the binding (and dissociation) mechanism is not
complex. There is an order of magnitude change in the
E. coli
concentration in solution
as one goes from the immunosensor with PAPG (10
7
CFU/ml) (
Abu-Rabesh et al.,
2009
) to the antibody-conjugated magnetic beads (10
8
CFU/ml) (
Lee et al., 2009
). Also,
no dissociation is exhibited during the binding of 10
7
CFU/ml
E. coli
in solution to the
immunosensor. This indicates that either the binding in this case is strong enough to pre-
vent the dissociation or the
E. coli
concentration is low. It is also seen that the fractal
dimension exhibited during the binding of 10
8
CFU/ml
E. coli
in solution to the anti-
body-conjugated magnetic beads is higher by 18.14% when compared with the fractal
dimension exhibited during the binding of 10
7
CFU/ml in solution to the immunosensor.
The fractal dimension is based on a log scale and even small changes in the value of the
fractal dimension represent significant changes in the degree of heterogeneity on the
biosensor surface.
(2) An electrochemical aptamer-based assay coupled to magnetic beads or the detection of
thrombin (
Centi et al., 2008
), and an EIS biosensor for analyzing aptamer-thrombin
interfacial interactions (
Li et al., 2008
)
A comparison of the binding and dissociation of 60 nM thrombin in solution to an EIS
biosensor (
Figure 6.4
;
Li et al., 2008
) with the binding of 20 nM thrombin in solution
to the biotinylated aptamer immobilized on a CMB chip (
Centietal.,2008
)indicates
that in one case there is binding and dissociation, and in the other just binding. On
comparing the binding phase kinetics for both these biosensor systems that are ade-
quately described by a single-fractal analysis, it is observed that as one goes from
the CMB chip (
Centietal.,2008
) to the EIS biosensor (
Li et al., 2008
), the fractal
dimension in the binding phase decreases by 24.1% from a value of
D
f
equal to
2.38632 to
D
f
equal to 1.810, and the corresponding binding rate coefficient increases
byafactorof47.9%fromavalueof
k
equal to 83.044 to
k
equal to 122.88. In this
case, a lower fractal dimension leads to a higher binding rate coefficient. This is con-
trary to the general trend presented in the different chapters throughout the topic.
However, it should be borne in mind that we are comparing and analyzing the perfor-
mance of two different biosensors which are detecting the same analyte (albeit of dif-
ferent concentrations; 20 and 60 nm).
(3) An ultrasensitive enhanced CL enzyme immunoassay for detecting AFP which was
amplified by double-codified gold nanoparticle labels (
Yang et al., 2009
), and a LSPCF
fiber-optic biosensor to detect AFP in human serum (
Chang et al., 2009
).
A comparison of the binding and dissociation rate coefficients and the corresponding fractal
dimension values for the binding and dissociation of AFP in solution
รพ
PIP to the double-
codified gold nanoparticle labels modified by HRP-conjugated anti-AFP (
Yang et al.,
