PANI-ZnO clad modified multimode optical fiber pH sensor based on EWA

In the present investigation, an intrinsic intensity modulated optical fiber pH sensor is developed and experimentally tested at room temperature. To fabricate the sensor probe, original cladding of multimode fiber was replaced by a pH-sensitive polyaniline-zinc oxide (PANI-ZnO) nanocomposite matrix whose absorbance property and refractive index (RI) are pH dependent. The synthesized PANI, ZnO, and incorporation of ZnO into PANI was confirmed and analyzed by some characterization techniques. It was observed that the ZnO composition into PANI not only enhances the materials's optical activity, porosity and hence sensitivity of the sensor but also boosts the mechanical strength of the coating layer over silica surface. Moreover, high index ZnO material is used to enhance the evanescent field towards the sensing region, which can help in better interaction of light from the outer medium. The pH sensing principle depends upon evanescent wave absorption (EWA) due to swelling/shrinkage of PANI and hence modification in volume and RI of the layer leads to change in transmitted optical power. The average sensitivity of proposed sensor was found to be 2.46 μW/pH for a wide pH range of 2–10 unit. The sensor also possesses excellent stability, fast response time, low hysteresis, good repeatability and durability characteristics. Results suggest that this sensor can be productively utilized in biomedical and chemical sensing applications.