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).
References
[1]
Lemos, S.G.; Nogueira, A.R.A.; Torre-Neto, A.; Parra, A.; Alonso, J. Soil calcium and pH monitoring sensor system. J. Agric. Food Chem. 2007, 55, 4658–4663.
[2]
Gu, B.; Yin, M.-J.; Zhang, A.P.; Qian, J.-W.; He, S. Low-cost high-performance fiber-optic pH sensor based on thin-core fiber modal interferometer. Opt. Express 2009, 17, 22296–22302.
[3]
Yin, M.; Gu, B.; Zhao, Q.; Qian, J.; Zhang, A.; An, Q.; He, S. Highly sensitive and fast responsive fiber-optic modal interferometric pH sensor based on polyelectrolyte complex and polyelectrolyte self-assembled nanocoating. Anal. Bioanal. Chem. 2011, 399, 3623–3631.
[4]
Yin, M.; Gu, B.; Qian, J.; Zhang, A.P.; An, Q.; He, S. Highly sensitive and selective fiber-optic modal interferometric sensor for detecting trace mercury ion in aqueous solution. Anal. Methods 2012, 4, 1292–1297.
[5]
Michie, W.C.; Culshaw, B.; Konstantaki, M.; McKenzie, I.; Kelly, S.; Graham, N.B.; Moran, C. Distributed pH and water detection using fiber-optic sensors and hydrogels. J. Lightwave Technol. 1995, 13, 1415–1420.
[6]
Jones, T.P.; Porter, M.D. Optical pH sensor based on the chemical modification of a porous polymer film. Anal. Chem. 1988, 60, 404–406.
[7]
Wolfbeis, O.S.; Offenbacher, H. Fluorescence sensor for monitoring ionic strength and physiological pH values. Sens. Actuators B. 1986, 9, 85–91.
[8]
Hammond, P.T. Form and function in multilayer assembly: New applications at the nanoscale. Adv. Mater. 2004, 16, 1271–1293.
Yin, M.; Qian, J.; An, Q.; Zhao, Q.; Gui, Z.; Li, J. Polyelectrolyte layer-by-layer self-assembly at vibration condition and the pervaporation performance of assembly multilayer films in dehydration of isopropanol. J. Membr. Sci. 2010, 358, 43–50.
[11]
Itano, K.; Choi, J.Y.; Rubner, M.F. Mechanism of the pH-induced discontinuous swelling/deswelling transitions of poly(allylamine hydrochloride)-containing polyelectrolyte multilayer films. Macromolecules 2005, 38, 3450–3460.
[12]
Goicoechea, J.; Zamarreno, C.R.; Matias, I.R.; Arregui, F.J. Utilization of white light interferometry in pH sensing applications by mean of the fabrication of nanostructured cavities. Sens. Actuators B. 2009, 138, 613–618.
[13]
Corres, J.M.; Villar, D.I.; Matias, I.R.; Arregui, F.J. Fiber-optic pH-sensors in long-period fiber gratings using electrostatic self-assembly. Opt. Lett. 2007, 32, 29–31.
[14]
Shao, L.-Y.; Jiang, Q.; Albert, J. Fiber optic pressure sensing with conforming elastomers. Appl. Opt. 2010, 49, 6784–6788.
[15]
Zhang, P.; Qian, J.; An, Q.; Du, B.; Liu, X.; Zhao, Q. Influences of solution property and charge density on the self-assembly behavior of water-insoluble polyelectrolyte sulfonated poly(sulphone) sodium salts. Langmuir 2008, 24, 2110–2117.
[16]
Zhao, Q.; Qian, J.; An, Q.; Gui, Z.; Jin, H.; Yin, M. Pervaporation dehydration of isopropanol using homogeneous polyelectrolyte complex membranes of poly(diallyldimethylammonium chloride)/sodium carboxymethyl cellulose. J. Membr. Sci. 2009, 329, 175–182.
[17]
Wang, L.Y.; Wang, Z.Q.; Zhang, X.; Shen, J.C.; Chi, L.F.; Fuchs, H. A new approach for the fabrication of an alternating multilayer film of poly(4-vinylpyridine) and poly(acrylic acid) based on hydrogen bonding. Macromol. Rapid Commun. 1997, 18, 509–514.
[18]
McAloney, R.A.; Sinyor, M.; Dudnik, V.; Goh, M.C. Atomic force microscopy studies of salt effects on polyelectrolyte multilayer film morphology. Langmuir 2001, 17, 6655–6663.
[19]
Yang, Y.-H.; Haile, M.; Park, Y.T.; Malek, F.A.; Grunlan, J.C. Super gas barrier of all-polymer multilayer thin films. Macromolecules 2011, 44, 1450–1459.
[20]
Burke, S.E.; Barrett, C.J. pH-dependent loading and release behavior of small hydrophilic molecules in weak polyelectrolyte multilayer films. Macromolecules 2004, 37, 5375–5384.
[21]
Jesus, M.C.; Ignacio, R.M.; Ignacio, D.V.; Francisco, J.A. Design of pH sensors in long-period fiber gratings using polymeric nanocoatings. Sens. J. 2007, 7, 455–463.
[22]
Miao, Y.-P.; Liu, B.; Zhao, Q.-D. Refractive index sensor based on measuring the transmission power of tilted fiber Bragg grating. Opt. Fiber Technol. 2009, 15, 233–236.
[23]
Zamarreno, C.R.; Bravo, J.; Goicoechea, J.; Matias, I.R.; Arregui, F.J. Response time enhancement of pH sensing films by means of hydrophilic nanostructured coatings. Sens. Actuators B. 2007, 128, 138–144.
