An Exposed-Core Grapefruit Fibers Based Surface Plasmon Resonance Sensor

To solve the problem of air hole coating and analyte filling in microstructured optical fiber-based surface plasmon resonance (SPR) sensors, we designed an exposed-core grapefruit fiber (EC-GFs)-based SPR sensor. The exposed section of the EC-GF is coated with a SPR, supporting thin silver film, which can sense the analyte in the external environment. The asymmetrically coated fiber can support two separate resonance peaks (x- and y-polarized peaks) with orthogonal polarizations and x-polarized peak, providing a much higher peak loss than y-polarized, also the x-polarized peak has higher wavelength and amplitude sensitivities. A large analyte refractive index (RI) range from 1.33 to 1.42 is calculated to investigate the sensing performance of the sensor, and an extremely high wavelength sensitivity of 13,500 nm/refractive index unit (RIU) is obtained. The silver layer thickness, which may affect the sensing performance, is also discussed. This work can provide a reference for developing a high sensitivity, real-time, fast-response, and distributed SPR RI sensor

Surface plasmon resonance sensing: an optical fibre based SPR platform with scattered light interrogation

This thesis describes the development, fabrication and optimisation of a Surface Plasmon Resonance (SPR) sensing architecture based on optical fibres. Motivated by biosensing applications, SPR was chosen as a simple and sensitive label-free technique that allows real time quantitative measurements of biomolecular interactions. Unlike conventional fibre SPR probes, this platform utilises a novel interrogation mechanism based on the analysis of scattered radiation facilitated by a rough plasmonic coating. A theoretical study is performed in order to determine the optimal parameters of the sensing configuration, i. e. the metal coating and fibre material. This analysis revealed a trade-off between the sensitivity of these devices, and their resolution. Optical fibres with cores made of lower refractive index materials were found to increase the sensitivity of the sensor, but broaden the SPR spectral signature. This broadening of the linewidth results in an unwanted increase in the sensor resolution, which leads to an undesirable increase in the detection limit. Therefore, experiments were performed to investigate the trade off between the sensitivity and resolution of the sensor to optimise both performance characteristics. The experimental demonstration and characterisation of a scattering SPR platform based on lead silicate fibres is described. The plasmonic coating with required surface roughness was fabricated using chemical electroless plating. In order to increase the refractive index sensitivity, a fibre SPR sensor with a lower refractive index core made of fused silica was produced. Due to the different surface properties of the silica glass and the lead silicate glass, surface modification with stannous chloride was required to fabricate suitable plasmonic coatings on the fused silica fibres. Characterisation of the new fused silica SPR sensors showed that the sensitivity of the sensing probe was improved, however, the spectral linewidth of the SPR signature was broadened, in agreement with the theoretical modelling. Nevertheless, analysis of the capability of the silica fibre based SPR sensors demonstrated potential for this platform in biological studies. To improve the resolution without affecting the sensitivity of a sensor, smaller core fibres can be used. However, using conventional small core fibres or fibre tapers is challenging due to their fragility and the requirement for fibre post processing to access the core. To overcome these difficulties, an SPR sensor based on a silica microstructured optical fibre with a core exposed along the entire fibre length was fabricated. Exposed Core Fibres (ECFs) have small cores that are supported by thin struts inside of a larger support structure, providing mechanical robustness to the fibre. The ECF SPR sensing platform doubled the improvement in the spectral linewidth when compared to the large core fused silica fibre sensor, without compromising sensitivity. Finally, the demonstration of Metal Enhanced Fluorescence (MEF) phenomena is presented. The effect of rough metallic coatings on the enhancement of fluorescence emission is investigated in planar glass substrates, showing significant improvement in emission when compared to smooth metal films. An optical fibre based MEF platform was demonstrated to illustrate the potential of rough metal coatings on a fibre for surface enhanced optical phenomena. This work is the first systematic study of a scattering based SPR sensing platform. This architecture addresses existing practical limitations associated with current SPR technologies, including but not limited to bulk design and affordability. Additionally, performance enhancement of the sensing probes is achieved through the use of alternative fibre material and geometry. The demonstrated performance improvements are not class-leading compared to commercial biosensing devices, however, the performance is in agreement with the theoretical analysis which provides a pathway for further improvement. This demonstrated that the scattering based SPR fibre platform is a practical new approach that offers the advantages of high sensitivity and signal to noise ratio, and low resolution, with the capability to improve the detection limit of SPR devices. Most importantly, this novel SPR interrogation approach allows the incorporation of two different sensing techniques, SPR and fluorescence, in the same fibre device, which opens pathways for novel biosensing applications combining the two phenomena.Thesis (Ph.D.)--University of Adelaide, School of Physical Sciences, 2017