Optimisation of Coating Protocols for Etched Fibre Bragg Grating Sensors and Applications in Sensing

Abstract

Fibre Bragg grating sensors, characterised by high sensitivity, flexibility, and immunity to electromagnetic interference, have found applications in commercial-grade temperature and strain sensors. Removing the clad, partially or entirely, and a subsequent functional coating provide etched Fibre Bragg grating (eFBG) sensors with an additional evanescent sensing capability. The eFBG sensors, despite their enhanced sensitivity, small footprint, and multimodal & multiplexing capability, face a significant challenge in reproducing the uniform functional coating. This thesis addresses the issue of obtaining reproducible functional coatings on eFBG sensors. As a demonstration of the efficacy of functionalised FBGs, few bio-sensing applications have been demonstrated. In this thesis work, appropriate coating techniques, including drop cast, spin, and electrospinning methods, are adopted to give a uniform coating on the eFBG sensor depending on the functionalisation material (chemical compound, 2D, and polymer). The performance of the coating is evaluated by an application that is biological or chemical. The sensor performance is characterised by sensitivity, dynamic range, specificity, reproducibility, and long-term stability. This thesis demonstrates that adopting the proper coating protocol enables the eFBG sensor to function in a non-traditional way. The bifunctionality of eFBG, both for drug delivery and measurement of the delivered dosage, are demonstrated. The multiplexing of this feature and imaging, like endoscopes, on a single optic fibre can translate eFBG sensors as a standalone platform for non-invasive targeted drug delivery, measurement of delivery effectiveness, and imaging of the targeted cell.