Optical sensor for pH monitoring using a layer-by-layer deposition technique emphasizing enhanced stability and re-usability (original) (raw)
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2012
In this work, the design and characteristics of a wavelength-dependent pH optical sensor have been studied. To create the sensor itself, brilliant yellow (BY) as a pH indicator and poly (allylamine hydrochloride) [PAH] as a cross-linker have been deposited on the end of a bare silica core of an optical fibre by use of a 'layer-by-layer' technique. In the experiments carried out to characterize the sensor, it was observed that the value of pK a (the dissociation constant) of the thin film is dependent both on the outer layer and the number of bilayers. A heat treatment process was applied to the sensor to reduce the effect on the deposited layers during the testing of the probe. As a result of these series of experiments, it could be concluded that the probe design on which were deposited structured layers comprising six double layers of (PAH/BY) showed the best sensitivity for a pH range from 6.80 to 9.00 (with an accuracy of ±0.20) and showing an average wavelength shift of 4.65 nm per 0.2 pH units, while the concentration of the BY and the PAH solutions was maintained as 0.25mM and 2.5mM respectively.
pH sensor based on a detection sol–gel layer onto optical fiber
Materials Science and Engineering: C, 2002
A pH sensor was made via the deposition of detection layer onto an optical fiber. This layer contains a pH-sensitive dye [thymol blue (TB)] trapped within a sol -gel silica matrix. The light was launched directly at the front of the fiber with an angle chosen in order to increase the power transmitted by the evanescent wave. This technique was used to induce the absorption of the dye. TB can be used both as an acid or a base titration indicator. However, the response of the optical device in acid conditions is rather poor and only the alkaline transition in the pH range 8 -12 has been exploited. The dye appears to be firmly trapped within the silica matrix and no leaching is observed during repetitive experiments. D 2002 Published by Elsevier Science B.V.
The pH sensor based optical fiber coated with PAH/PAA
Journal of Physics: Conference Series, 2019
pH-sensitive optical fiber sensors were fabricated with layer-by-layer (LbL) method. Multiple layers of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) bilayers were coated on an unclad fiber to create the pH-sensitive region. The coating process was done using a coating system developed in this work. 10 to 40 bilayers of PAH/PAA were coated on the fiber core to evaluate its performance as pH sensor. The existences of coating on the fiber were verified with field emission scanning electron microscopy (FESEM) and energy-dispersive x-ray spectroscopy (EDX) analysis. It was shown that the fabricated sensor is pH sensitive and independent of variation in the refractive index of the surrounding. The best performance was obtained with 30 bilayers fiber sensor. The sensitivity and resolution of the sensor were 0.453 a.u/pH and 0.0022 pH units respectively. With the developed coating system, various physical and chemical sensors can be realized by varying the coating mater...
Response time enhancement of pH sensing films by means of hydrophilic nanostructured coatings
Sensors and Actuators B: Chemical, 2007
This work describes the improvement in response time of thin film optical fluorescent sensors for pH detection based on the 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) pH-sensitive molecule. Two different kinds of structures were fabricated to demonstrate these concepts, using the electrostatic layer-by-layer (LbL) assembly method. These structures were built up on both glass slides and tapered ends of standard communications optical fiber substrates. The basic structures are based on a sensitive coating formed by the alternate deposition of the polymer poly(allylamine hydrochloride) (PAH) as the cationic monolayers and the polymer poly(acrylic acid) (PAA) and the fluorescent pH indicator HPTS as the anionic monolayers. These sensitive coatings showed a long response time when they were immersed in different pHs. In order to improve the performance of basic devices one approach was followed, which consisted of the deposition of a highly hydrophilic block before the sensitive coating. These enhanced devices were proved to decrease the response time dramatically. AFM and water contact angle measurements showed that properties of these structures including the hydrophilic block had higher roughness and lower contact angle (around 10 • ) whereas the ones without the hydrophilic block were smoother and had higher contact angles (around 50 • ). The response time of both devices was also measured while the pH was changed several times resulting in a remarkable reduction with the new devices. The most significant reduction was in rise time response between pH 3 and pH 7 which was five times minimized.
Fast and long term optical sensors for pH based on sol–gels
Analytica Chimica Acta, 2003
Long lasting and fast response optical sensor for the detection of pH in the range of 6-12 is described. The sensor is fabricated by spin coating silica sol in the presence of phenol red (PR). The sol is in turn obtained by acidic hydrolysis of tetraethoxysilane (TEOS) and phenyltriethoxysilane (Ph-TriEOS). The performance of the sensor depends on the ratio of Ph-TriOES to TEOS. At the optimal composition, the sensor has a response time of less than 20 s, the response is completely reversible and its lifetime is over 12 months.
Fiber-optic pH sensors fabrication based on selective deposition of Neutral Red
2009 IEEE Sensors, 2009
In this work, a novel application of the electric field directed layer-by-layer self assembly (EFDLA) selective deposition method for the fabrication of optical fiber pH sensors is presented. Here, indium tin oxide (ITO) coated optical fibers have been fabricated via a dip-coating deposition method. These fibers are used as electrodes in the EFDLA protocol in order to deposit selectively the sensitive layer. Neutral Red (NR) colorimetric pH sensitive indicator and the polymers poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) are used in order to obtain a pH sensitive nanostructured coating onto ITO coated optical fibers. The results obtained in this work revealed that the LbL material adsorption on the electrodes can be enhanced or even inhibited when applying a specific direct current voltage between them under some other specific fabrication parameters. Particularly, the response of these sensors to variations of the pH in the surrounding medium was studied when the pH of the solutions used for the fabrication of the films was adjusted to 7.0 and the potential applied between electrodes was set to 2.5 V. These sensors showed fast response time and high repeatability.
pH sensor based on sol-gel silica layer deposited on a plastic optical fiber with blue bromophenol
2004
Design and characterization of a pH optical fiber sensor with a pH sensitive dye is described in this paper. TEOS (Tetra-ethyl-Orto-Silicate) was used to dope a plastic optical fiber, which will be used as the optical probe (OPTRODE). The sensor is prepared by fixing the doped plastic fiber on a fused ortosilica block surface with blue bromophenol. The fiber surface charged with silica modified the refractive index, which plays an important roll on the fiber, modifies the conditions of light propagation into the plastic optical fiber. The fiber transmittance is used to measure the pH of a solution or a fluid in a range between 4 and 7; such signal is captured by a photodetector and processed with a LabView program. The advantage of this system is that, 2cm of doped fiber are enough to measure the pH of a fluid in real time. The time response of the sensor reported in the present study is approximately 10s.
Sensors and Actuators B: Chemical, 2008
A new pH optical sensor for a wide pH range was prepared by chemical immobilization of a mixture of two indicators of Neutral Red and Thionin on an agarose film coated glass slide (ACGS). For preparation of the sensor, the two dyes were immobilized on an epoxy activated agarose support and the effects of the coupling pH and the dyes ratio and concentrations were optimized. The sensor was mounted in a flow cell and successfully applied for on-line pH monitoring in a wide pH range of 0.5-12 with two linear calibration curve regions. The pH sensor could perform fast response (within 1-2 min) and longterm stability (continuous use for at least 3 months) with no evidence of dye leaching. The sample ionic strengths up to 0.5 mol L −1 did not significantly influence the responses. A reproducibly better than 0.20% (R.S.D.) was obtained for 6 replicated pH measurements.
Design of pH Sensors in Long-Period Fiber Gratings Using Polymeric Nanocoatings
IEEE Sensors Journal, 2000
In this paper, two different pH sensors based on the deposition of nanometric scale polymeric films onto the surface of a long-period fiber grating (LPFG) have been studied and compared. An electrostatic self-assembled (ESA) method has been used to create sensitive films with an optimal overlay thickness. Two types of sensors have been designed: The first one is based on polyallylamine hydrochloride (PAH), polyacrylic acid (PAA), and the second one was done incorporating the pigment Prussian blue (PB) in the PAH/PAA matrix. A theoretical model of multilayer cylindrical waveguides based on coupled-mode theory has been used to predict the position of the attenuation bands as a function of the overlay thickness. Both sensors were tested and compared in terms of sensitivity and response time. A faster response was obtained with the introduction of PB particles in the polymeric matrix. Linear sensors in the pH range 4-7 were obtained, showing good repeatability and high sensitivity.
pH sensor based on sol-gel silica layer deposited on a plastic optical fiber with blue bromophenol
Photonics North 2004: Photonic Applications in Telecommunications, Sensors, Software, and Lasers, 2004
Design and characterization of a pH optical fiber sensor with a pH sensitive dye is described in this paper. TEOS (Tetra-ethyl-Orto-Silicate) was used to dope a plastic optical fiber, which will be used as the optical probe (OPTRODE). The sensor is prepared by fixing the doped plastic fiber on a fused ortosilica block surface with blue bromophenol. The fiber surface charged with silica modified the refractive index, which plays an important roll on the fiber, modifies the conditions of light propagation into the plastic optical fiber. The fiber transmittance is used to measure the pH of a solution or a fluid in a range between 4 and 7; such signal is captured by a photodetector and processed with a LabView program. The advantage of this system is that, 2cm of doped fiber are enough to measure the pH of a fluid in real time. The time response of the sensor reported in the present study is approximately 10s.