Wide-range and highly sensitive pH sensor based on a figure-eight fiber structure coated with copper/polyvinyl alcohol hydrogel

Abstract

Construction of pH sensors based on optical fiber encapsulated copper (Cu-NPs) has been accomplished. Briefly, a length of single-mode fiber (SMF) of about 25 cm has been wrapped in two rings by twisting one side of the fiber on the other from both ends to form a figure-eight shape. To upsurge the sensitivity, the sensor configuration has been immobilized with copper nanoparticles/polyvinyl alcohol hydrogel (Cu/PVA) composite. The Cu/PVA composite was employed to shape a membrane structure on the sensing active length by laminating it using the dip-coating method. The wavelength interrogation method was employed to evaluate the sensitivity of the fabricated pH sensor. The fabricated fiber pH sensor exhibits a sigmoidal response above a wide range of pH from 1 to 14. The result displays a superior sensitivity of ∼4.8 nm/pH for a range of 1-7 pH and 3.86 nm/pH for the range of 8-14 pH with an excellent linear response. Besides the great sensitivity, the dual-parameters measurement of pH and refractive index was effectively accomplished with perfect stability. The proposed fiber sensor possesses a superior performance compared with the other sensors.