Introduction

1. Ru(dpp) Nanoparticles 5 % O2 10 % O2 atm 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@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@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) a) b) c) d) 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 RBITC Nanoparticles 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. 10 % SO2 10 % SO2 20 % SO2 RBITC & Ru(dpp) Dual Sensor Fig 4: Response to SO2 and O2 of dual film 420 nm ex 350 nm ex 10 % SO2 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. 10 % O2 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.