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Sensors 2013, 13(2), 1425-1434; doi:10.3390/s130201425

Fiber Optic pH Sensor with Self-Assembled Polymer Multilayer Nanocoatings

1,2,* , 2
1 Institute of Optoelectronic Technology, China Jiliang University, Hangzhou 310018, China 2 Department of Electrical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 3 Department of Electronics, Carleton University, Ottawa, ON K1S 5B6, Canada
* Author to whom correspondence should be addressed.
Received: 7 December 2012 / Revised: 16 January 2013 / Accepted: 21 January 2013 / Published: 24 January 2013
(This article belongs to the Section Physical Sensors)
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A fiber-optic pH sensor based on a tilted fiber Bragg grating (TFBG) with electrostatic self-assembly multilayer sensing film is presented. The pH sensitive polymeric film, poly(diallyldimethylammonium chloride) (PDDA) and poly(acrylic acid) (PAA) was deposited on the circumference of the TFBG with the layer-by-layer (LbL) electrostatic self-assembly technique. The PDDA/PAA film exhibits a reduction in refractive index by swelling in different pH solutions. This effect results in wavelength shifts and transmission changes in the spectrum of the TFBG. The peak amplitude of the dominant spectral fringes over a certain window of the transmission spectrum, obtained by FFT analysis, has a near-linear pH sensitivity of 117 arbitrary unit (a.u.)/pH unit and an accuracy of ±1 a.u. (in the range of pH 4.66 to pH 6.02). The thickness and surface morphology of the sensing multilayer film were characterized to investigate their effects on the sensor’s performance. The dynamic response of the sensor also has been studied (10 s rise time and 18 s fall time for a sensor with six bilayers of PDDA/PAA).
Keywords: fiber-optic sensor; layer-by-layer self-assembly; multilayer film; pH sensor; tilted fiber Bragg grating fiber-optic sensor; layer-by-layer self-assembly; multilayer film; pH sensor; tilted fiber Bragg grating
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Shao, L.-Y.; Yin, M.-J.; Tam, H.-Y.; Albert, J. Fiber Optic pH Sensor with Self-Assembled Polymer Multilayer Nanocoatings. Sensors 2013, 13, 1425-1434.

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