We report the development of a plastic optical fiber (POF) sensor modified by molecular imprinting for ammonium sensing.
A molecularly imprinted polymer (MIP) grafted on the surface of the optical fiber by radical polymerization with thermal initiation served as a sensitive layer. The POF’s selected for this study are a polymethyl methacrylate (PMMA) based step-index optical fiber with 1 mm.
Firstly, initiator 2,2'-Azobis(2- ethylpropionamidine)dihydrochloride was immobilized on the surface of the uncladded fiber. Grafting of the polymer was carried out using methacrylic acid as a monomer, ethylene glycol dimethacrylate as a cross- linker, ammonium chloride as a template and 30% of ethanol in water as a solvent.
Optimization of the polymerization condition including reagent concentrations and polymerization time was optimized using thickness of the grafted imprinted polymer layer as a criterion. Deposition of the polymer was inspected using optical microscopy and measurements with micrometer.
A transmission based detection scheme was implemented using an optical coupler (90:10), a LED (660 nm) and two photodetectors. The signal output was monitored in real time with LabView software. Measurements made during fiber modification have shown that immobilization of initiator does not affect transmission while MIP grafting decrease it. Response of the optical fiber with grafted MIP layer to ammonium ions in water solutions has been observed.
Further developments will be focused on the optimization of MIP grafting procedure and sensor performance.