Design and investigation of a novel 𝝿-configuration spr sensor for multi-parameter biosensing applications.

Early, precise, and accessible diagnostics are among the most pressing challenges in current global health and biomedical engineering. Cancers, and viral infections all manifest as distinct biomarkers with vanishingly low quantities at the critical, treatable outset of illness. Conventional diagnostic procedures are fundamental but have significant limitations. They frequently involve time-consuming, multi-step processes, necessitate costly labels that can affect biomolecular behaviour, and typically test only a single analyte at once. Furthermore, their sensitivity levels are typically insufficient for early detection in complex biological matrices. Optical biosensors based on Surface Plasmon Resonance (SPR) principles have emerged as a viable alternative, allowing for real-time, label-free molecular interaction monitoring. However, widespread adoption of conventional SPR platforms has been hampered by their susceptibility to environmental drift, limited sensitivity, and fundamental inability to extract more than a single signal parameter from a binding event. This diagnostic landscape highlights a critical and unmet need. The design of a novel ϖ-configuration SPR biosensor with rigorous theoretical investigations addresses this multifaceted challenge. The foundational contribution is the conception and computational validation of this unique geometric architecture, which features two independent, adjacent sensing arms on a single optical fibre. Through comprehensive three-dimensional Finite Element Method (FEM) simulations in COMSOL Multiphysics, this work establishes the ϖ-sensor's core optical performance. The ϖ-configuration sensor showed an exceptional sensitivity of 3300 nm/RIU for silver-coated sensing regions that analysed Refractive Index (RI) changes from 1.37 to 1.38. This is a 120% improvement over the 1500 nm/RIU attained by the D-shaped equivalent. Further investigations also demonstrated how strategic material asymmetry across the sensing regions of the ϖ-sensor can be engineered to encode dual, independent channels within a single transmission spectrum. The investigation featured a bimetallic asymmetry (Ag/Au) setup, which utilises the natural dispersion contrast between noble metals to perform spectral demultiplexing. This design produced two resolvable resonance dips, at 856 nm (Ag) and 912 nm (Au), with sensitivities of 8100 nm/RIU and 7700 nm/RIU, respectively for an analyte RI of 1.41. The integration of metal-dielectric (Ag-TiO2) in one sensing region induced a significant red shift of 294 nm, enabling wavelength-division multiplexing (WDM) for simultaneous dual-analyte detection. TiO2's high refractive index enhanced the local evanescent field, boosting sensitivity from 12,600 nm/RIU in the Ag-analyte region to 20,000 nm/RIU in Ag-TiO2-analyte region. Furthermore, through nanoscale multilayer surface engineering, the sensor was modified to increase its sensing capabilities. Computational investigations were carried out to study the effect of a sophisticated tripartite layered stack, Ag/TiO₂/Gr, on the sensitivity of the sensor. The Ag thin film serves as the primary plasmonic exciter, the TiO2 layer act as a dielectric waveguide spacer, shifting the resonance and extending the evanescent field decay length to increase the sensing volume, while the graphene monolayer provides exceptional molecular adsorption by locally intensifying the electric field due to its infinite surface conductivity. The Ag/TiO₂/Gr design achieved a maximum sensitivity of 21200 nm/RIU, a 68.3% increase over Ag/Ag film and a 6% increase over Ag/TiO₂ bilayers. Finally, investigations also showed that this multilayer architecture facilitates multiparameter sensing utilizing two orthogonal output signals: resonance wavelength shift Δλ, and resonance broadening ΔFWHM. This dual output results from the intricate interaction of field confinement and loss. This body of work illustrates a clear progression from a novel photonic concept to a sophisticated sensor. The investigations, through a hierarchical design strategy, that incorporates innovative geometry, material-based multiplexing, and nanoscale interfacial engineering for a ϖ-sensor hereby sees the design of a versatile sensor capable of high-sensitivity, multi-parameter, and multi-analyte label-free detection for specialized biosensing applications.

Author dc:creator

• Ehiabhili, John

Advisor dc:contributor.advisor

• S. Kannan and P. Radhakrishna

• Surface plasmon resonance
• Fibre optic sensor
• ϖ-configuration
• Multi-analyte detection
• Multiparameter sensing
• Multilayer structure
• Thin films

Language dc:language

en

Identifier

oai:rgu-repository.worktribe.com:3463797
https://doi.org/10.48526/rgu-wt-3463797

OAI identifier oai:identifier

oai:rgu-repository.worktribe.com:3463797