Santos, AbelAbell, AndrewStanley, NathanLaw, Cheryl SuwenTran, Nhu Khoa2025-06-122025-06-122025https://hdl.handle.net/2440/145131Advances in sensing technologies have revolutionised the way gases are detected and monitored, enabling the development of tools that cater to the growing need for precise, real-time data in various applications. Among these, optical gas sensors have emerged as a promising solution by offering high sensitivity, molecular-level selectivity, compact designs, and non-intrusive sensing capabilities, while also addressing key limitations of conventional sensors, including long-term signal drift, cross-sensitivity to non-target analytes, and the need for frequent calibration. Additionally, optical gas sensors developed based on nanoporous materials open avenues for integration into lab-on-a-chip devices, providing a transformative potential for miniaturised, portable gas sensing solutions. As the demand for cost-competitive, accurate, and highly-integrable sensing systems grows, the development of next-generation gas sensors is vital to meet the requirements of diverse applications, from large-scale industrial systems to portable personal monitoring devices. In this context, this thesis explores the development of optical gas sensors based on nanoporous anodic alumina (NAA), focusing on the implementation of NAA-based photonic crystals (NAA–PCs) and functional materials. The fabrication of these NAA-based optical sensors was achieved through the structural engineering of NAA–PCs using electrochemical oxidation (i.e., anodisation) of aluminium. The porosity of these structures was tailored using pulse-like anodisation strategies to optimise optical properties and efficiently harness distinct forms of light–matter interactions at the nanoscale. The sensing characteristics of NAA optical sensing systems, in terms of selectivity and sensitivity, were further engineered by functionalising these porous platforms with different functional molecules. Various optical sensing mechanisms—including refractive index shifts, resonance band modulation, and random lasing—were systematically investigated and demonstrated through real-time detection of volatile organic compounds (VOCs) and other gases and vapours. The ability of NAA optical sensors to discriminate between different gases and vapours was also investigated by analysing the dynamic optical signal responses associated with each gas or vapor. The work completed in this thesis demonstrated that: (i) NAA–PCs are versatile and compact platforms to harness distinct forms of light–matter interactions for gas sensing applications; (ii) engineering the structure and porosity of NAA–PCs via anodisation enables precise tuning of optical properties to optimise light–matter interactions, resulting in tailored optical signals and structures with unique multiple outputs; (iii) functionalisation of NAA–PCs with diverse sensing materials, such as quantum dots and analyte-specific chemical modifiers, enhances the selectivity through tailored interaction of the sensing platform with target gases; and (iv) the optical signals produced by NAA-based sensors can be analysed to identify the fingerprints of different gases based on their unique physical and chemical interactions with the sensing platform. The findings from this work establish a framework for the precise design of NAA-based optical sensors, advancing both the fundamental understanding and applied knowledge of the gas sensing performance of NAA–PCs with optimised geometrical, chemical, and optical properties. These advancements unlock the transformative potential of the developed optical gas sensing systems to evolve into fully functional and marketable analytical tools for real-world applications in environmental monitoring, industrial safety, and medical diagnostics.enNanoporous Anodic AluminaPhotonic CrystalsOptical Gas SensorDiscrimination Gas SensorThesis