Biomedical Engineering Reference
In-Depth Information
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0.01
0.05
0.09
0.22
0.44
0.88
2.63
Immobilization capacity (Max [GST], nmol)
FIGURE 11.8
Conjugation product yield obtained from each of the immobilized enzyme chips. Absorbance values were meas-
ured after a 1-min reaction on a colorimetric substrate. The X -axis indicates the immobilization capacity for each
chip as calculated using a simple geometric model for PSi.
Interpore distance
D
Pore diameter
d
Pore height
( D)
z
FIGURE 11.9
Simple geometric model for calculating
PSi internal volume.
Second, other aspects of the immobilization process, from sample handling to simple
contact with the PSi surface, may render some fraction of the enzyme inactive through
denaturation or other degradation. Finally, the microenvironment of the PSi matrix itself
may contribute to diminished activity, through charge effects (unmodified silicon is anion-
ically charged at neutral pH 32 ) or by sterically impeding diffusion. In the context of
biosensing, all of these effects can potentially interfere with performance of the sensor, and
will require further study.
With an understanding of the immobilization capacity and enzymatic performance of
GST-functionalized PSi devices in hand, we could next proceed with correlating these
observations with the changes in optical spectra that are the hallmark of PSi biosen-
sors. 33
For a series of devices prepared with increasing concentrations of GST, we were
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