Biomedical Engineering Reference
In-Depth Information
TABLE 11.1
Comparison of Immobilized vs. Solution GST Enzyme Activity for Fixed Substrate
Concentrations
Solution [GST] (nmol)
GST (
g/ml)
Activity (nmol/min)
Specific activity
(
mol/(min mg))
Solution Enzyme Reaction
0.05
33
10.8
4.3
0.10
67
19.4
3.9
0.50
333
49.2
2.0
Immobilized Enzyme Reaction
0.05
33
2.6
1.0
0.10
67
4.7
0.9
0.50
333
26.2
1.0
1.00
667
48.5
1.0
Note
: Glutathione = 3.3 mM; CDNB = 3.3 mM.
0.80
25
20
0.60
15
0.40
10
0.20
5
0
0.00
0
0.5
1
1.5
2
2.5
Immobilized GST concentration (nmole)
FIGURE 11.10
Correlation of sensor response with enzyme activity. The microcavity detection limit appears to lie between 0.1
and 0.5 nmol of GST.
gratified to observe a strong correlation between enzyme activity and optical response,
as measured by redshift in the reflectance spectrum (Figure 11.10). The observation that
the optical response is linear, while the enzymatic performance becomes nonlinear at
high concentration, is interesting and potentially a reflection of the increased probabil-
ity of active-site occlusion that occurs when higher concentrations of enzyme are immo-
bilized. Despite being a relatively simple observation this places the use of PSi as a
matrix for the construction of biosensors on firmer experimental footing. Simulations
conducted during the course of this work suggested that devices tuned to operate closer
to the infrared should have improved sensitivity; this assertion remains to be tested.
