There is vast amount of research carried out on the production of fluorescent sensors. We have produced novel sensors by incorporation of fluorescent dyes (known as fluorophores) into silica nanoparticles. The sensor works by the detected species

1
Improvement of Thin Film Gas Detectors by
Incorporation of Novel Nanoparticles A. Farooq,
R. Al-Jowder, Dr R. Narayanaswamy and Dr D.
Whitehead Diversion of Chemistry Materials,
Faculty of Science Engineering, Manchester
Metropolitan University, Chester Street,
Manchester, M1 5GD. Contact a.farooq_at_mmu.ac.uk
Introduction There is vast amount of research
carried out on the production of fluorescent
sensors. We have produced novel sensors by
incorporation of fluorescent dyes (known as
fluorophores) into silica nanoparticles. The
sensor works by the detected species quenching
the fluorophores luminescence. The sensing
capabilities can be manipulated by selecting the
appropriate fluorophore as they bind to specific
gases1. The objective of this work is to produce
an enhanced dual sensor that works simultaneously
in detecting sulphur dioxide (SO2) and (oxygen)
O2 gases. The fluorophore rhodamine B
isothiocyanate (RBITC) will be used to produce a
nanosensor that is sensitive to SO2, while
ruthenium-tris(4,7-diphenyl-1,10-phenanthroline)
dichloride (Ru(dpp)) will be used to sense O2.
The fluorophore itself is by no means sufficient
in giving the sensor its action the matrix it
exists in also plays an important role. These
nanosensors will be encapsulated in an
organically modified sol-gels (ormosil) matrix.
The surface of nanoparticles is modified with
carboxylic acid groups to anchor to the ormosil
matrix. The Ru(dpp) and RBITC nanosensor
produced a significantly high response to gases
along with response recovery. The monodispersed
nanoparticles sizes ranged from 200 nm-400 nm.
The carboxylic acid functionalization of dye
modified silica nanoparticles was preformed by
the ring opening reaction of succinic anhydride
subsequently attaching to the amine group. A
thin film was produced onto a glass slide
combining different dye encapsulated in one
sol-gel matrix film producing a dual sensor that
capable of detecting SO2 and O2 simultaneously
using luminescence spectroscopy.
Experimental   Synthesis of dye silica
nanoparticles   Silica nanoparticles were
synthesised using Stöber method. The reaction
entails the hydrolysis and condensation of TEOS
in aqueous solution of ethanol and water. The
dyes were trapped in the nanoparticles by
incorporating it in Stöber method. Silica
nanoparticles were synthesised using the
procedure describes by Verhaegh et al2 and then a
seeding technique. NH4OH (2 ml) was added to
EtOH (24 ml) and stirred. The dye (1 mg) and APS
(0.01 ml) mixture was placed in the mixture and
further stirred. Finally a solution of TEOS (1.5
ml) and ethanol (6 ml) was added to mixture and
allowed to stir for 24 hr causing the solution to
become opaque. A shell was grown on the seeds to
obtain the required diameter.

  Functionalising the SiO2 nanoparticles
with carboxylic acid The carboxylic acid
functionalised silica nanoparticles were prepared
using Yanqing An et al method3. APS (0.4 ml) was
added to the SiO2_at_dye nanoparticles and stirred
for 20 h. The nanoparticles were cleaned by
centrifugation to remove any un-reacted
reactants. DMF (25 ml) was mixed with the
nanoparticles and added to a mixture of DMF (25
ml) and succinic anhydride (0.25 g). The
solution was allowed to stir for 24 hr and
further cleaned by centrifugation.

 Scanning Electron Microscopy (SEM)
Fig 1 SEM images of nanosensor SiO2 particles.
RBITC containing nanoparticles a) 200 nm and b)
278 nm. Ru(dpp) containing nanoparticles c) 200
nm and d) 390 nm.

Testing the Sensor using Luminescence
Spectroscopy A thin film was prepared by drying
the nanosensor particles onto a glass slide.
Ormosil was spin coated onto the nanoparticles to
produce a continuous film. The film was placed
into a test chamber under vacuum and luminescence
was obtained whilst exposing to the test gasses.
The results for exposure of RBITC to SO2 are
shown in figures 2. The luminescence was quenched
when exposed to 10 and 20 test gas. The
results for exposure of Ru(dpp) to O2 are shown
in figures 3. The luminescence was quenched when
exposed to 5 and 10 test gas. In figure 4 the
results of a duel sensor thin film are shown.
The Ru(dpp) and RBITC nanosensor produced a
significantly fast and sensitive response to the
test gases. The response recovery time was also
quick proving the viability of the sensor.
Scheme 1 Incorporation of the dye within the
silica nanoparicles.
Fig 2 Luminescence of RBITC film response to SO2
Scheme 2 Synthesis of the dye modified silica
nanoparticles functionalised with carboxylic acid.
Fig 3 Luminescence of Ru(dpp) film response to
O2
Results and Discussion Verhaegh et al found
that when RBITC dye was not modified with APS and
used in an alcohol solution it did not
incorporate into the silica. This is because APS
couples to the dye and silica preventing any loss
of the dye when it further reacts with ammonia.
The dye APS mixture was stirred for 4 hr under N2
atmosphere in a dark room the colour changed from
an intense purple to orange as self-quenching has
occurred. Therefore we coupled RBITC and Ru(dpp)
dye with APS, and found both dyes incorporated
onto the silica nanoparticles. When TEOS is
hydrolysis by ammonia, shown in scheme 1, it
causing ethoxy groups to be substituted for
hydroxyl groups. Therefore it become hydrophilic
like the dyes and causing it to be trapped in the
nanoparticles. Monodispersed carboxylic
functionalised RBITC-silica nanoparticles with a
diameter of a) 200 nm, b) 278 nm and Ru(dpp)
functionalised-silica nanoparticles with a
diameter of c) 200 nm and d) 390 nm were
successfully synthesised and SEM images are shown
in figure 1.
Fig 4 Response to SO2 and O2 of dual film
Conclusions A RBITC-SiO2 and Ru(dpp)-SiO2 dual
sensor was successfully synthesized. These
nanosensors produced a significantly fast and
sensitive response to the test gases. The
response recovery time was also quick proving the
viability of the sensor.
References 1. P. J. R. Roche, R. Al-Jowder, R.
Narayanaswamy, J. Young and P. Scully A novel
luminescent lifetime-based optrode for the
detection of gaseous and dissolved oxygen
utilising a mixed ormosil matrix containing
ruthenium (4, 7-diphenyl-1, 10-phenanthroline)3Cl2
(Ru.dpp), Anal Bioanal Chem, 2006, 386,
1245-1257. 2. N. A. M. Verhaegh and A. van
Blaaderen Dispersions of Rhodamine-Labeled
Silica Spheres Synthesis, Characterization, and
Fluorescence Confocal Scanning Laser Microscopy,
Langmuir, 1994, 10, 1427-1438. 3. Y. An, M.
Chen, Q. Xue and W. Liu Preparation and
self-assembly of carboxylic acid-functionalized
silica, Journal of Colloid and Interface
Science, 2007, 311, 507-513.