Biomedical Engineering Reference
In-Depth Information
regions. In this case, the product (antibody-antigen; or analyte-receptor complex, Ab
Ag or
analyte
receptor) is given by:
<
t
ð
3
D
f1
,
bind
Þ=
2
¼ t
p
1
,
t < t
1
t
ð
3
D
f2
,
bind
Þ=
2
ð
Ab
Ag
Þ
t
p
2
,
ð
15
:
3
Þ
¼
t
1
<
t
<
t
2
¼
t
c
:
t
1
=
2
,
t
>
t
c
In some cases, as mentioned above, a triple-fractal analysis with six parameters (
k
1
,
k
2
,
k
3
,
D
f1
,
D
f2
, and
D
f3
) may be required to adequately model the binding kinetics. This is when
the binding curve exhibits convolutions and complexities in its shape due perhaps to the very
dilute nature of the analyte (in some of the cases to be presented) or for some other reasons.
Also, in some cases, a dual-fractal analysis may be required to describe the dissociation
kinetics.
15.3 Results
We now present a fractal analysis of the binding and dissociation (if applicable) of the kinet-
ics of (a) CEA in glucose using enzyme-catalyzed deposition of a redox polymer and electro-
lytic oxidation of ascorbic acid (AA) (
Gao et al., 2009
), (b) TNF-
a
using poly(guanine)
functionalized silica nanoparticles (NPs) (
Wang et al., 2006
), (c) binding of IgG-antithrombin
in solution to immobilized biotinylated thrombin, and binding of thrombin in solution to
immobilized biotinylated aptamer (
Centi et al., 2008
), (d) binding of cholesterol to a choles-
terol biosensor (
Shin and Liu, 2007
), (e) binding and dissociation of the protein biomarker,
protein specific antigen (PSA) to different gold nanocrystals for different immunoprobe con-
centrations in solution (
Cao et al., 2009
), (f) binding of the transcription factors (rhSP1 and
rhNF-
k
B) to oligonucleotides on a microcantilever array (
Huber et al., 2006
), and (g) binding
and dissociation of different concentrations of thrombin in solution to the best aptamer in
generation 4 (G4.0422) immobilized on a SA chip (
Platt et al., 2009a,b
).
Gao et al. (2009)
have recently developed a doubly amplified electrochemical immunoassay
(EIA) for the detection of CEA. Their assay uses enzyme-catalyzed deposition of a redox
polymer and electrolytic oxidation of AA by the deposited redox polymer. This is a dual-
amplification scheme that enhances analytical signals.
Gao et al. (2009)
have expressed the need to detect a few key proteins at the POC such as in
clinics and in doctors' offices (
Emili and Cagney, 2000; Mcbeath, 2002; Mitchell, 2002
).
They further propose that electrochemical biosensors may be used to measure different
analytes in blood without interference from blood cells, proteins, and fat globules (
Yao
et al., 1995; Hirsch et al., 2003
). They have developed a dual amplification scheme in EIA
to detect a colon cancer biomarker, CEA and claim that the detection limit and sensitivity
are far superior to the previous biosensor detection devices.
