Wavelength dependent pH optical sensor using the layer-by (original) (raw)
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Sensors and Actuators B: Chemical, 2014
Stable and reliable operation of an optical sensor for pH monitoring is important for many industrial applications of these types of devices. The layer-by-layer deposition technique is a simple and versatile method used to deposit a sensitive thin film on such an optical fibre-based device but creating a coating which can often be destroyed in use in highly acid or alkali solutions i.e. with very low or very high pH. It is thus important to create stable and durable sensors to meet the needs of users for operation under these extreme environments. The main aim of this study has been to prepare a number of such sensors and compare the performance of three different stabilization approaches used for the development of an effective wavelength-dependent pH-sensitive optical sensor. Techniques such as employing heat treatment, the deposition of two layers of a PAH/SiO 2 thin film and the deposition of two layers of APTMS/SiO 2 as topping layers have been studied to determine the optimum approach to creating a stable and reliable sensor-one yielding the same value of peak wavelength for a measurement of a known value of pH and to do so repeatibly. An improvement in performance and in shelf-life, stability and re-usability of the sensor has been achieved by the addition of two bilayers of APTMS/SiO 2 (3-Aminopropyl-trimethoxy silane/Silica nanoparticle) in the work carried out and the results of the investigation undertaken are reported.
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...
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.
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.
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.
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.
International Journal of Electrical & Electronic Systems Research (IEESR), 2019
The fabrication and characterization of an optical fiber pH sensor for the detection range 2 – 7 are described. The sensing element was prepared by coating the uncladded middle portion of a multimode plastic clad silica fiber (PCF) with xerogel film of immobilized bromophenol blue (BPB) prepared by a sol-gel process. The exponential decay of the evanescent wave at the core-cladding interface of the multimode fiber was utilized to determine the pH response. The objective of this work is to analyze the measurement of the fiber optic sensing probe towards various pH level. The intensity of the absorbance was analyzed using statistical technique (Statistical Package for the Social Sciences, SPSS) to identify the significant pH range that can be used as a reference in developing the sensor instrumentation in the future. pH2 shows the highest significance among all pH values based on the statistical results using error plots.
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.