Biomedical Engineering Reference
In-Depth Information
150
bias
: 1.0 V
: 1.3 V
: 1.5 V
y = 10.87x + 21.5
( R = 0.991 )
100
y = 8.77x - 13.3
( R = 0.990 )
50
y = 1.74x -2.57
( R =
0
.938 )
0
0.0
2.0
4.0
6.0
8.0
10
12
14
pH
Fig. 4.25.
Calibration curves at various fixed bias against various pH levels. The
calibration curves were calculated from
CV
characteristics to varied pH solutions
at a fixed bias, as described in the figure
made of acetylcellulose, the membrane was easy to handle and store. Storage
of a microbial membrane in the 1 mM phosphate buffer (pH 7) containing
0.15 M of NaCl at 4
◦
C kept its activity for more than 14 weeks.
Optimization of the Conditions of the System.
Biosensors that mea-
sure pH shift have a large dependence on the buffer ability. A high buffer
ability inhibits the pH shift at the sensor surface and reduces the sensiti-
vity, but a low buffer ability makes the response unstable. Figure 4.26 shows
the dependence of the response on the concentration of the buffer. A lower
concentration of the buffer gave a larger response, and even the lowest con-
centration, 1.0 mM, showed enough stability.
Various concentrations of BOD solution (0-500 ppm) were applied to the
system to obtain a calibration curve as shown in Fig. 4.27. A BOD stan-
dard solution containing glucose (150 mg/l) and glutamic acid (150 mg/l)
was employed as a model wastewater, according to the Japanese Industrial
Standard (JIS). The BOD response increased with increasing BOD concen-
tration of the standard solution in a linear relationship between the decrease
of the photocurrent (BOD response) and the BOD concentration from 0 to
100 ppm (
r
=0
.
988).
Comparison with BOD
S
and BOD
5
.
The SPV-based sensor also mea-
sured the BOD value for various kinds of organic substances. Table 4.2 sum-
marizes the substrate specificity of the SPV method, compared with reported
data of BOD
5
(five-day method) and BOD
S
(sensor method) for the various
compounds [61]. For the organic substances, including lactose, soluble starch,
