Chemistry Reference
In-Depth Information
Fig. 5.8 The response time
of the holographic glucose
sensor. When 1.0 and
10.0 mM glucose were added
into the reservoir, the sensor
equilibrated in
*
1hat24
°
C
(micro
flea, 2 mm). The sensor was reset using acetic acid (10 mol%, v/v). Other
acids that will decrease the pH can also be used. The same sensor may therefore be
used for repeat analyses. To demonstrate the sensitivity of the sensor, concentra-
tions <1.0 mM were analysed. As the concentration of glucose increased from 0.0
to 1.0 mM under physiological conditions (pH 7.4, IS = 150 mM, 24
fl
C), the Bragg
peak of the holographic sensor systematically shifted from 507 to 532 nm
(Fig.
5.7
c). The Bragg peak shift and glucose concentration are linearly correlated
(Fig.
5.7
d), allowing the determination of glucose <1.0 mM.
The readouts of the holographic glucose sensor were reproducible. Consecutive
swelling/shrinking steps were reproducible to within
°
3 nm over 10 successive
buffer changes after equilibrium was reached. No noticeable hysteresis was
detected. Additionally, the sensor
±
'
s response was measured in real time for both 1.0
and 10.0 mM glucose (Fig.
5.8
). Measurements at low glucose concentrations
(<1 mM) required
90 % equilibrium, whereas measurements at
higher glucose concentrations (>1 mM) required shorter times (
70 min to reach
*
*
50 min) to reach
*
90 % equilibrium. The Bragg peak returned to the original position when PBS
was added and equilibrated in
*
1 h. The apparent pK
a
value of the poly(AAm-co-
*
3-APB) matrix was
8.5 based on the Henderson-Hasselbalch equation, while the
sensor displayed improved sensitivity as the pH was increased from 7.0 to 9.5
(Fig.
5.9
, see inset for the colorimetric readouts).
*
5.5.2 Holographic Glucose Sensor Readouts in Arti
cial
Urine
Arti
cial urine solutions were prepared as reported previously [
45
]. Two stock
solutions (500 mL) of arti
cial urine were prepared with and without glucose
(10.0 mM). The solutions were
filtered (pore size = 0.22
μ
m). The pH was adjusted
