Chemistry Reference
In-Depth Information
to glucose, lactate and fructose molecules as well as other carbohydrates such as
xylose, galactose, maltose, ribose, mannose, lactose and sucrose [
18
]. Urine
consists of many carbohydrates including maltose, lactose,
D
-mannose,
D
-glucose,
D
-ribose,
D
-xylose,
L
-arabinose and
D
-galactose [
59
]. The Bragg peak shift
in
holographic sensor readouts can be expressed as:
D
k
tot
¼
D
k
glu
þ
D
k
lact
þ
D
k
fru
þ
D
k
carbo
D
k
IS
ð
Þ
5
:
13
where
D
k
carbo
are the red Bragg peak shifts due to glucose,
lactate, and fructose and other carbohydrates, and
D
k
lac
; D
k
fruc
and
ʔʻ
IS
is the blue Bragg peak shift
due to increase in IS from a standard molarity reference. Since the Bragg peak shift
readouts were a combination of many other carbohydrates, elimination of these
interferents may be required for accurate analyses.
Glucose sensors comprising of optical transducers embedded into analyte-
responsive materials are attractive for the development of healthcare monitoring
systems [
46
,
60
]. The advantages of optical sensors over traditional dyes [
61
],
fl
fluorescent molecules [
62
,
63
] and electrochemical [
64
67
] assays are that they:
-
(i) are not affected by electromagnetic
fields, (ii) are label-free, (iii) enable sterile
remote sensing, (iv) are amenable to miniaturisation and multiplexing, and (v) are
able to be used in real-time continuous monitoring [
68
]. Notable optical sensors
have included photonic structures such as plasmonic nanomaterials [
69
], hybrid
nanogels [
70
], photonic crystalline colloidal arrays [
71
], and inverse opal hydrogels
[
72
]. These analyte-responsive polymers have the added advantage of
fine tuning
through a change in periodic structure, index of refraction and/or localised surface
plasmon resonance. Although these polymeric optical sensors can be microfabri-
cated, self-assembled or a combination of both; there is currently no rapid, low-cost
and generic sensor fabrication technique capable of producing narrow-band,
uniform, reversible colorimetric readouts with a high-tunability range. The chapter
showed a holographic sensor, which was fabricated using laser light to allow
forming Bragg gratings in a rapid manner. While the range of spectral readouts was
finely controlled by changing the wavelength of the laser light and the chemistry of
the exposure bath; the sensitivity of the photonic sensor was modulated by varying
the concentration of the crosslinker and the functional groups in the hydrogel
matrix. The kinetic theory developed in this chapter is based on the correlation of
slope with the
first proposed methodology for inferring
concentrations of target analytes within minutes. This approach can be applied to
any hydrogel-based sensor or polymeric nanoparticle-based drugs for the optimi-
sation of binding kinetics. Many diagnostic approaches have utilised boronic acid
derivatives in the development of fluorescence, colorimetric, electrochemical and
optical sensors [
46
,
60
,
73
,
74
]. The advantage of the present study over these
sensors is that holographic sensors produced by the rapid photochemical patterning
offers routes to incorporate two or 3D images into the hydrogel matrix. For
example, photomasks or 3D objects can be used during laser writing to produce
user-friendly fool-proof text/quantity-reporting capabilities. The holographic sens-
ing platform has
final readout, and it is the
fl
flexibility in controlling the angle of off-axis diffraction precisely
