Biomedical Engineering Reference
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binding kinetics. The values of the binding rate coefficient k and the fractal dimension D f for
a single-fractal analysis are given in Table 15.1 .
Shin and Liu (2007) have recently developed a screen-printed cholesterol biosensor. These
authors compared the performance of gold (Au) and platinum (Pt) as the working electrode
material. A self-assembly approach was used to fabricate the biosensor. These authors indi-
cate that both the gold and the platinum would detect the cholesterol in solution through
the electrochemical oxidation of H 2 O 2 . However, the authors selected gold as the working
electrode material as it exhibited a higher response current and better sensitivity. The enzyme
cholesterol oxidase (Chox, E.C. 1.1.3.6) was immobilized on the Au working electrode by
using a self-assembly approach. The authors report that their thick-film screen-printed cho-
lesterol biosensor comprises three electrodes on an alumina-substrate. 3-mercaptopropionic
acid (MPA) was self-assembled onto the gold working electrode and formed a thin organic
layer. This thin layer of MPA served as an anchor for enzyme immobilization.
Figure 15.4a shows the binding of 20 mg/dl cholesterol in solution to the cholesterol biosen-
sor. A single-fractal analysis is adequate to describe the binding kinetics. The values of the
binding rate coefficient k and the fractal dimension D f are given in Table 15.2 .
Figure 15.4b shows the binding of 100 mg/dl cholesterol in solution to the cholesterol biosen-
sor. A dual-fractal analysis is required to adequately describe the binding kinetics. The values
of (a) the binding rate coefficient k and the fractal dimension D f for a single-fractal analysis,
and (b) the binding rate coefficients k 1 and k 2 and the fractal dimensions D f1 and D f2 for a
dual-fractal analysis are given in Table 15.2 .
0.35
0.25
0.3
0.2
0.25
0.15
0.2
0.15
0.1
0.1
0.05
0.05
0
0 0
10
20
Time (min)
30
40
0
10
20
Time (min)
30
40
B
A
Figure 15.4
Binding of different concentrations of cholesterol (in mg/dl) to a cholesterol biosensor
( Shin and Liu, 2007 ): (a) 20
Continued
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