Development and characterisation of optical fibre-based pH sensor

Background This study presents the development and characterisation of an optical fibre coated with silver nanoparticles and silica composite for pH measurement, where pH corresponds to the negative log of hydrogen ions in solution.Methods A fabrication process, including sol–gel synthesis, optimisation of the coating formulation and adhesion, controlled etching of the optical fibre to a diameter of 104 ± 1 µm, and thermal treatment to enhance the optical signal and stability, was systematically developed. The etched fibre diameter was varied, and an optimal core diameter of ~104 µm was identified, providing a favourable balance between light intensity and leakage from the fibre.Results The sensor showed repeatability within a pH range of 3 to 11 based on conventional potentiometric pH measurements. A calibration technique showed a good relationship between the optical response and solution pH, which validated the accuracy and reliability of the optical response.Conclusions Practical issues, such as batch-to-batch variability, coating defects, and manufacturability, were analysed, and mitigation strategies were proposed. The stability of the sensor by comparing the pH values on the first and tenth day due to dissolution of the coating from the fibre.