Chemistry Reference
In-Depth Information
manufacturing remains a signi
cant challenge. Improvement of such technologies
can enable rapid point-of-care diagnostics, particularly in the developing world,
where rapid tests are not affordable. For example, Abbott Laboratories markets the
i-STAT system, a handheld device that integrates micro
uidics and electrochemical
detection to analyse blood chemistry [
40
]. i-STAT quanti
fl
es analytes such as
electrolytes, metabolites, and gases, while also having the capability to perform
immunoassays. However, its high price and dependence on cartridges limits its
potential for low-cost rapid diagnostics.
In this chapter, a porhyrin derivative was synthesised to produce a NP-free
holographic metal ion sensor. The porphyrin molecule served purposes such as
crosslinking of the HEMA monomers, light absorption during grating fabrication, as
well as chelating agent for cation sensing. The holographic sensor was fabricated with
a fraction of time and complexity when as compared to other grating fabrication
techniques [
75
78
]. The sensor was used to quantify the concentrations of organic
solvents in water, and used porphyrin as a chelating agent to quantify Cu
2+
and Fe
2+
ions in solutions. The sensor diffracted narrow-band light in the visible region
enabling visual readouts for solvent measurements in water. However, the sensor was
insensitive to low concentration of metal cations since the amount of porphyrin
derivative in the polymer matrix served as the chelating agent as well as the cross-
linker, which limited the swelling of the polymer matrix. The design of pendant
porphyrin derivatives may increase the sensitivity and allow the pHEMA matrix
swell to enable colorimetric readouts in the entire visible spectrum. In terms of
fabrication
-
flexibility, the diffraction angle and the holographic pattern (e.g. photo-
masks) can be controlled depending on the desired application. Additionally, the laser
writing technique described in this chapter can be used to pattern nanostructures on
various surfaces [
79
,
80
]. Holography also allows fabrication and printing of sensors
in three-dimensional networks of hydrophobic materials (e.g. poly(dimethylsiloxane)
(PDMS)) and polyacrylamide or hybrid polymers [
81
fl
84
]. Holographic sensors can
be functionalised to be sensitive to many analytes such as pH, metal ions, glucose,
lactate and fructose [
85
-
89
]. It is envisioned that holographic sensors will be
incorporated in multiplex micro
-
fl
uidic devices, contact lenses and wearable devices
[
40
,
90
ed
using smartphones and smartwatches [
94
,
95
]. Holographic sensing is label-free,
which not only serves as an analyte receptor, but also an optical transducer for
colorimetric readouts. The porphyrin-based holographic sensor may
93
]. Since holographic sensors are colorimetric, they might be quanti
-
find applications
from environmental monitoring to biochemical detection.
References
1. Yetisen AK, Qasim MM, Nosheen S, Wilkinson TD, Lowe CR (2014) Pulsed laser writing of
holographic nanosensors. J Mater Chem C 2(18):3569
3576. doi:
10.1039/C3tc32507e
2. Ala A, Walker AP, Ashkan K, Dooley JS, Schilsky ML (2007) Wilson
-
'
s disease. Lancet 369
(9559):397
408. doi:
10.1016/S0140-6736(07)60196-2
-
