Chemistry Reference
In-Depth Information
350 mJ), directed at the sample elevated at 5
°
from the surface plane and backed by a
mirror (object) (Fig.
5.4
c).
Analysis of the NP size distribution, angular measurements and determination of
apparent pK
a
value of the hydrogel matrix in combination with computational
modelling of optical properties allowed optimisation and utilisation of the diffrac-
tion properties for sensing applications. TEM imaging was used to estimate the NP
size distribution in the matrix. The holographic glucose sensor had a diffraction
grating consisting of Ag
0
NPs (
*
ø
15
25 nm) organised by the multi-beam
-
interference of a single 6 ns laser (
m
thick pAAm matrix functionalised with 3-APB. Figure
5.5
a, b illustrates the cross
sectional images of Ag
0
NP impregnated poly(AAm-co-3-APB) matrix before and
after photochemical patterning, respectively. The Ag
0
NPs after single-pulse laser-
induced photochemical patterning reduced in size as illustrated by the TEM images
of the transverse plane of the matrix. Figure
5.5
c, d shows the NP thresholds set for
size distribution analysis for Fig.
5.5
a, b, respectively. Figure
5.5
e
ʻ
= 532 nm, 200 mJ) pulse within a
10
μ
*
i illustrates the
matrix before and after patterning, respectively. Figure
5.6
shows the distribution of
Ag
0
NPs across the cross section of the matrix. The images of the Ag
0
NPs in situ
showed the reduction of size from
-
9 nm (n = 221)
before and after patterning, respectively. The changes in particle size, density and
periodicity of the Ag
0
NPs de
ø
17
±
11 nm (n = 83) to
ø
10
±
'
ned the sensor
s spectral response to the intensity
and diffraction at different wavelengths.
5.5 Holographic Glucose Sensors for Urinalysis
The measurement of urine glucose has diagnostic applicability in a number of
clinically relevant conditions [
30
]. Under normal conditions, the excretion rate of
glucose in urine ranges between 0.30 and 1.70 mmol/24 h [
7
]. Since most
filtered
glucose is normally reabsorbed, an elevated urine glucose concentration indicates
either impaired tubular reabsorption of glucose (e.g. familial renal glycosuria), or
more commonly, hyperglycemia that exceeds the kidney
s reabsorptive capacity
(e.g. diabetes mellitus) [
31
,
32
]. Conversely, a low concentration of urine glucose
may be found in urinary tract infections due to the bacterial metabolism of glucose
[
33
]. Existing colorimetric and electrochemical tests are based on the glucose
oxidase reaction [
34
,
35
]. However, their performance in detecting undiagnosed
diabetes is limited due to low sensitivity (i.e. correctly identi
'
ed patients with
disease), which ranges from 21 to 64 % [
36
39
]. False negative readings occur due
to high detection limits and interference from medications (Table
5.3
)[
40
,
41
].
While low-sensitivity tests may be useful [
42
], false negatives can lead to a false
sense of safety among users, and more critically delay correct diagnosis and early
treatment [
38
,
43
].
-
