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

Diseño y caracterización de estructuras resonantes y estrategias de concentración avanzada aplicadasa dispositivos fotónicos

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Óptica, leída el 23-09-2020Efficient low-cost optoelectronic devices are used for many applications, for example, energy production, and sensing. The development of these devices can be step-forward using nanophotonic and nanoplasmonic structures. In this dissertation we propose, design, and analyze several nanostructures to improve the performance of these devices. For energy applications, we select amorphous silicon hydrogenated, and perovskite/crystallinesilicon tandem solar cells. We choose amorphous silicon solar cells because this material is abundant, non-toxic, long-life compared to organic solar cells, and can be fabricated at a low cost. The tandem perovskite/crystalline silicon solar cells are devices with potential power conversion efficiency > 30 %. Our designs are based on dielectric nanostructures. We applied a 1D nanostructure array to the top and bottom of amorphous silicon hydrogenated solar cells, in two separate designs. The absorption enhancement within the auxiliary layers of these devices is dissipated as heat and partially mitigate the defects resulted from the Staebler Wronski effect. A metasurface in the form of multilayer gratings embedded in the active layer of the perovskite top cell of the tandem device, improves the absorption efficiency in the whole device. A sawtooth periodic back texture has been optimized and tested to work with the metasurfacef or further improvement of the device performance. These nanostructures are arranged to maximize the absorption efficiency of the selected solar cells, mainly by reducing their total reflectance. The analysis and calculations are completed by modeling the conditions of the sun illumination, i.e, unpolarized light, and oblique incidence. The performance of the devices is calculated under these conditions...Los dispositivos optoelectrónicos eficientes y de bajo coste se utilizan en muchas aplicaciones. Por ejemplo, en la producción de energía y en sensores. La incorporacion de estructuras nanofotónicas y nanoplasmónicas es un paso adelante en el desarrollo de estos dispositivos. En esta tesis doctoral proponemos, diseñamos y analizamos varias nano-estructuras que mejoran el rendimiento de estos dispositivos. En aplicaciones para energía, hemos selecionado células de silicio amorfo hidrogenado, y células tándem de perovskitas y silicio cristalino. Hemos elegido las células solares de silicio cristalino porque es un material abundante, no tóxico, de larga vida comparada con las células orgánicas y fabricadas a bajo coste. Las células tándem perovskita/silicio cristalino son dispositivos con eficiencias de conversión superiores al 30 %. Nuestros diseños están basados en nano-estructuras dieléctricas. Hemos aplicado una nano-estructura periódica 1D a la superficie anterior y posterior de células solares de silicio amorfo hidrogenado en dos diseños separados. El aumento de la absorción en las capas auxiliares de estas células se disipa como calor y mitiga parcialmente los defectos producidos por el efecto Staebler-Wronski. Una metasuperficie hecha con redes apiladas en capas incluidas en las capa activa de la porción superior de una célula tándem mejora la eficiencia de absorción de todo el dispositivo...Fac. de Ciencias FísicasTRUEunpu

A Whispering Gallery Mode Microlaser Biosensor

A biological sensor, commonly referred to simply as a biosensor, is a transducing device that allows quantitative information about specific interactions, analytes or other biological parameters to be monitored and recorded. The development of biosensors that are low-cost, reliable and simple to use stand to facilitate fundamental breakthroughs and revolutionize current medial diagnostic methods. Notably, there remains an unmet need for developing in-vivo biosensors, allowing insights to be directly gained from the precise location of biological interactions within the human body. Over the last two decades, whispering gallery modes (WGM) within microresonators have emerged as a promising technology for developing highly sensitive and selective biosensors, among many other applications. However, significant work remains to allow WGM sensors to make the transition from primarily being used within purely research environments to real-world applications. Specifically, one of the key limiting factors is the requirement of an external phase-matched coupling scheme (such as a tapered or angle polished optical fiber, prism or waveguide) to excite the WGMs, despite these devices displaying tremendous sensing performance. One way to lift this dependency on complex interrogation schemes is introduce a gain medium, such as a fluorescent dye or coating the resonator with quantum dots for example, thereby rendering it active and allowing remote excitation and collection of the WGM spectrum. Using active WGM resonators has allows the creation of novel sensing opportunities such as tagging, tracking and monitoring forces from insides living cells. Applications like these could not have been realized using external phase-matched coupling schemes. The biosensing platform presented here is based on combining WGM within active microspherical resonators with microstructured optical fibers (MOF). The MOF enables both the excitation and collection method for the WGM spectrum while simultaneously providing a robust and easy to manipulate dip sensing architecture that has the potential to address the unmet need for real time labelfree in-vivo sensing by combining with a catheter. The platform is investigated fundamentally as well as experimentally, beginning with the development of an analytical model that is able to generate the WGM spectrum of active microspherical resonators. This provides the opportunity to pinpoint the optimal choice of resonator to be used for undertaking refractive index based biosensing. Specifically by being able to extract the quality (Q) factor, a measure of the resonance linewidth, and refractive index sensitivity from the WGM spectrum, the optimal combination of resonator parameters (diameter and resonator refractive index) can be identified for optimizing the resonators sensing performance. Further, the availability, biocompatibility and cost, as well as fabrication requirements can be also considered when selecting the ideal resonator. Next, the inherently lower Q-factors observed in active resonators compared to their passive counterparts (i.e. resonators without a gain medium) is examined using a combination of theoretical, experimental and imaging methods. Through this examination process, the inherent asphericity of the resonator is identified as being the limiting factor on the Q-factor of active resonators, with its effect most notably being observed for measurements made in the far field. Experimentally, the first demonstration of this platform operating as a biosensor is presented by monitoring the well-documented specific interaction of Biotin/neutravidin in pure solutions. Including identifying ways to improve sensing performance and lower the detection limit, such as operating the resonator above its lasing threshold. Although, it is noted that in its current form, this platform is best suited for the monitoring of protein, preferably occurring in higher concentrations, until further improvements to the sensing performance can be implemented. However, the robust design coupled with its ability to provide access to previously difficult to obtain locations provides an insight into its potential future application capabilities. Finally, the extension of the platform to operating in complex samples, namely undiluted human serum, is outlined. By self-referencing the platform, through the addition of a second, almost identical resonator (only varying in its surface functionalization) into one of the remaining vacant holes on the tip of the fiber, the effects of non-specific binding as well as changes in local environmental conditions (i.e. temperature fluctuations), can be eliminated.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 201

A Revised LRSPR Sensor with Sharp Reflection Spectrum

In this work, we have proposed a novel long-range surface plasmon resonance (LRSPR) sensor with sharp reflection spectrum, which consists of a glass prism, a (A/B)4-type waveguide-coupled layer and a metal layer. To reveal its sharp reflection spectrum perfectly, we have simulated the effects of all factors of this LRSPR sensor on the reflection spectrum, and finally presented the optimal parameters of the LRSPR sensor with sharp reflection spectrum