Chemistry Reference
In-Depth Information
Fig. 3.2 Fabrication of holographic sensors by in situ size reduction. a HEMA monomers,
ethylene dimethacrylate and methacrylic acid were copolymerised on an O
2
-plasma-treated
PMMA substrate. b Ag
+
ions were perfused into pHEMA matrix. c Using a photographic
developer, Ag
+
ions were reduced to Ag
0
NPs in the pHEMA matrix. Reprinted with permission
from Ref. [
18
] Copyright 2014 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim. d
-
e Patterning
the hydrogel matrix in
ection mode using a Nd:YAG pulsed laser. Reproduced
from Ref. [
24
] with permission from The Royal Society of Chemistry
“
Denisyuk
”
re
fl
photographic developer until no more darkening was seen (Fig.
3.2
c). The sample
was washed thoroughly with tap water, prior to immersion in acetic acid (5 % v/v)
to neutralise the developer. A levelled Petri dish, with a silver mirror in the bottom
surface, was
filled with ascorbic acid (unbuffered, 2 % w/v, pH 2.66) and with the
pHEMA side facing down, the sample was immersed in the bath at an inclination of
5. The pHEMA matrix remained in the Petri dish for 15 min to equilibrate. The
sample was exposed to a single 6 ns pulse, Q-switch delay set to 258
µ
s by Nd:
YAG pulsed laser (
λ
= 532 nm, 350 mJ) with a spot size of 2.5
3.5 cm (Fig.
3.2
d).
-
Figure
3.2
e shows the laser writing setup in Denisyuk re
fl
ection mode. In order to
produce holographic
flakes, the slides were immersed in water-ethanol solution
(50 %, v/v) for 1 h. After the
fl
floated off the PMMA slide, they were stored in
a glass Petri dish containing DI water to prevent sticking.
fl
akes
fl
3.3 Characterisation of Holographic pH Sensors
Holographic pH sensors fabricated by in situ size reduction of Ag
0
NP were
characterised. Optical and electron microscopes allowed investigating the size and
the distribution of Ag
0
NPs throughout the polymer matrix. Angular-resolved
measurements were taken to understand the sensor
'
s diffractive properties. Other
characterisation methods such as diffraction ef
ciency, index of refraction, and
surface roughness and thickness measurements were correlated with the micro-
graphs. Finally, limitations of this fabrication approach and its characterisation
methods were pointed out.
