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Enhanced fluorescence evanescent wave spectroscopy with integrated polymer optical waveguides.


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Abdul-Hadi, Jalal (2018). Enhanced fluorescence evanescent wave spectroscopy with integrated polymer optical waveguides. Thèse. Québec, Université du Québec, Institut national de la recherche scientifique, Doctorat en sciences de l'énergie et des matériaux, 231 p.

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Research in optical biosensors has gained great interest in the last two decades. Although many optical technologies were developed, integrated optics technologies revealed to be popular due to their potential for quick detection, highly sensitive measurements and particularly for miniaturization. Indeed, miniaturization of an optical sensing device offer the possibility to integrate it in a lab-on-a-chip (LOC) system. Which consists, in the best scenario, of a device that takes care of the delivery of the bio or chemical samples to the sensing area with microfluidic channels and treatment of the detection signal in a single chip with micro dimensions. Optical sensing structures with nano to micro dimensions can then be easily integrated with microfluidics, hence ideal for LOC devices. Also, they surpass electrochemical sensors for this task since they are immune to electromagnetic interferences which could alter the detection results. Optical sensing devices could be in many forms, but for the purpose of miniaturization channel waveguides are the best candidates. Indeed, the fabrication processes for channel waveguides benefited immensely from microelectronics circuits manufacturing technologies which have been refined for decades. In this work, polymer channel waveguides were used as the sensing platforms for evanescent wave fluorescence spectroscopy among other optical bio sensing methods because of its high sensitivity and specificity. Firstly, a novel fabrication process was developed for SU-8 polymer optical waveguides on a quartz substrate which revealed different characteristics than SU-8 polymer waveguides on a silica substrate fabricated with the standard protocol. They differed from each other mainly in their lower optical propagation losses and lower asymmetry. The SU-8 on quartz waveguides were then compared with the SU-8 on silica waveguides for evanescent wave fluorescence spectroscopy to investigate the impact of the different parameters from the novel and standard fabrication protocols. Finite difference time domain (FDTD) simulations were performed to evaluate the impact of the different asymmetries of both SU-8/quartz and SU-8/silica waveguide on the fluorescence collection efficiency for simulated emitting fluorophores. Also, an evanescent wave fluorescence spectroscopy experiment was performed with Alexa 647 labeled Bovine serum albumin (BSA) molecules to evaluate the sensitivity of both waveguides for fluorescence detection. In brief, the FDTD simulations showed an increase in the fluorescence collection efficiency for the SU-8/quartz waveguide compared to the SU- 8/silica waveguide and the experimental results revealed that the SU-8/quartz waveguide offered a greater sensitivity than the SU-8/silica waveguide. Moreover, to evaluate the impact of the variations of the different parameters (dimensions, core & substrate refractive indices) of both the SU-8/quartz and SU-8/silica waveguides on the fluorescence collection efficiency, a new calculation method was developed. This calculation method combined a modal propagation approach to find the fluorescence collection efficiency for planar waveguides with the effective index method. Finally, new geometries were designed with the purpose of increasing the area of immobilization of the labeled targets for increased sensitivity. Namely, the cascaded, doubled and tripled waveguides. The geometries of these new designs were first optimized for the excitation light propagation with numerical simulations (beam propagation method) and then by experimental characterization. Evanescent wave fluorescence spectroscopy experiments with Alexa 647 labeled biotin were performed to compare their performance with a single straight waveguide. The experimental results revealed increased sensitivity for the new designs compared to the straight waveguide. Concentrations of Alexa 647-biotin as low as 15, 9, 10 and 7 pg·mL-1 were detected for the single, cascaded, doubled and tripled waveguides respectively. Experimental results were expected to be higher, taking into account the increased area of immobilization. To understand this discrepancy, additional numerical simulations with the beam propagation method were performed to analyze the optical losses of the evanescently coupled fluorescence guided throughout the sensors.

Type de document: Thèse Thèse
Directeur de mémoire/thèse: Gauthier, Marc-André
Co-directeurs de mémoire/thèse: Packirisamy, Muthukumaran
Mots-clés libres: énergie et matériaux
Centre: Centre Énergie Matériaux Télécommunications
Date de dépôt: 25 juill. 2019 17:44
Dernière modification: 25 juill. 2019 17:44
URI: http://espace.inrs.ca/id/eprint/8448

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