Optimization of Coating Thickness on Optical fiber via Layer-by-Layer Technique for pH Sensing Application.

Layer-by-layer (LbL) coating system developed capable to monitor the LbL coating process on optical fiber for sensor application in real-time basis. The objective was to determine the optimum number of bilayer coatings for best sensing performance. Multiple layers of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were coated on the surface of optical fiber core to create pH sensitive coating. The real-time monitoring of absorbance spectrum during coating process from 0 to 50 bilayers of PAH/PAA were done. The existence of the coating on the fiber were verified using field emission scanning electron microscopy (FESEM) and energy dispersive x-ray spectroscopy (EDX). The monitoring results show that 30 bilayers of PAH/PAA coating has high absorbance of 0.87 OD. at 800 nm. The pH sensing performance of the fiber without PAH/PAA coating was compared with the 30 bilayers of PAH/PAA coated fiber. The best performance was obtained with 30 bilayers of PAH/PAA coated fiber with the sensitivity of 0.453 OD/pH and resolution of 0.0022 pH units. [ABSTRACT FROM AUTHOR]