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Ammonium sensing in aqueous solutions with plastic optical fiber modified by molecular imprinting

Sequeira, F. ; Duarte, D. ; Rudnitskaya, Rudnitskaya, A. ; S. R. Gomes, Gomes, M. T. S. R. ; Nogueira, R.N. ; Bilro, L.

Ammonium sensing in aqueous solutions with plastic optical fiber modified by molecular imprinting, Proc European Workshop on Optical Fibre Sensors - EWOFS, Limerick, Ireland, Vol. 9916, pp. 99161I-1 - 99161I-4, May, 2016.

Digital Object Identifier: 10.1117/12.2236941

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Abstract
We report the development of a low cost plastic optical fibre (POF) sensor for ammonium detection using molecularly
imprinted polymers (MIP’s). The cladding of a 1 mm diameter PMMA fiber is removed, in which is grafted a molecular
imprinted polymer (MIP), by radical polymerization with thermal initiation, that act as a selective sensing layer. For the
polymerization, 2,2’-Azobis(2-methylpropionamidine)dihydrochloride (AAPH) is used as initiator, methacrylic acid
(MAA) as a monomer, ethylene glycol dimethacrylate (EDMA) as a cross-linker, ammonium chloride (NH4Cl) as a
template and 30% of ethanol in water as a solvent.
The sensing method consists of an intensity based scheme. The response to different concentrations of ammonium solutions
in water has been evaluated at room temperature. Solutions with (0 - 0.6) M concentration, with the corresponding
refractive indexes varying between 1.3325 – 1.3387, at 25°C were used. The response of the fiber with the original
cladding, and after cladding removal has been monitored and compared to the response given by the developed sensor.
The response is very fast, less than 1 minute and reversible, which allows the continuum use of the sensor.
Further developments are focused in optimization of MIP grafting procedure and sensor performance, in order to increase
sensitivity.