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Fibre Optic pH Sensor Using Optimized Layer-by-Layer Coating Approach

Raoufi, N., Surre, F., Rajarajan, M. , Sun, T. & Grattan, K. T. V. (2013). Fibre Optic pH Sensor Using Optimized Layer-by-Layer Coating Approach. IEEE Sensors Journal, 14(1), pp. 47-54. doi: 10.1109/JSEN.2013.2280283


In this study the design and characterization of a high resolution wavelength dependent pH optical sensor fabricated using the layer-by-layer technique was undertaken. In this approach, brilliant yellow (BY) as a pH indicator and poly (allylamine hydrochloride) [PAH] as a cross-linker have been deposited on an uncladded silica fibre. A number of key parameters, such as the number of bilayers, the concentration of the BY solution and the shape of the fibre, as well as its core diameter have been varied with a view to optimizing the design and performance of the pH sensor. The results obtained from a series of evaluations show that the sensitivity was enhanced by reducing the concentration of the indicator solution used and by designing a U-bend configuration sensor probe with a sharply bent fibre. However, when making an overall comparison, the straight (unbent) fibre probe resulted in a more sensitive probe when compared to the use of a high radius bend. Further, utilizing a small core diameter of the fibre allows a wide pH range to be measured and with high sensitivity. Additionally, the performance was shown to be improved for measurements over a narrower range of pH, by using a fibre with a larger core diameter. Considering the effect of the number of layers, work carried out has shown that probes with 5-6 bilayers presented the best performance. The sensitivity has been shown to diminish when more than 6 layers were used and the sensing range shifts towards higher pH values. When monitored, the value of pKa (the dissociation constant) of the thin film showed the smallest change of any of the design factors considered. In summary, using a larger core diameter, employing a larger curve radius, a higher number of bilayers, a higher concentration of the indicator solution and applying PAH as an outer layer, all cause a higher pKa value and consequently the probe sensitivity moves towards alkaline region.

Publication Type: Article
Additional Information: © 2013 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting /republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
Publisher Keywords: layer-by-layer, optical sensor, pH measurement, U-bend sensor, chemical sensor
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Departments: School of Science & Technology > Engineering
School of Science & Technology > Engineering > Electrical & Electronic Engineering
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