Early-onset diagnostics, or the detection of disease before clinical symptoms arise, has gained traction for its potential to improve patient quality of life and health outcomes. Biosensors, found in point-of-care (POC) devices, facilitate early-onset diagnostics and disease monitoring by addressing the limitations of current diagnostics strategies, which include timeliness, cost-effectiveness, and accessibility. Biosensors often incorporate microarrays within their design to allow for the detection of disease-associated biomolecules, known as biomarkers. Microarrays are composed of capture biomolecules, such as monoclonal antibodies, that are immobilized through either contact or non-contact printing techniques. In the following thesis, we investigated microarray designs within novel biosensing platforms for diagnostic and disease monitoring applications. First, we highlighted the advantages and challenges of implementing different types of biosensors, detection methods, and biomolecule immobilization strategies. Additionally, we proposed a novel 3D microarray incorporating hydrogels composed purely of crosslinked bovine serum albumin (BSA) proteins decorated with capture antibodies (CAbs). Utilizing industry-standard inkjet printing, we developed and optimized a two-step fabrication protocol, by which BSA proteins and CAbs are printed first, followed by the crosslinking agent, 1-Ethyl-3-[3-dimethylaminopropyl]carbodiimide (EDC). Characterization of the unique three-dimensional (3D) microstructure and hydrogel parameters and conducting comparisons with standard two-dimensional (2D) microdots, showed that increasing biosensor surface area led to a 3X increase in signal amplification. The limits of detection (LODs) for cytokine biomarkers were 0.3pg/mL for interleukin-6 (IL-6) and 1pg/mL for tumor necrosis factor receptor I (TNF RI), which were highly sensitive compared to reported LODs from literature. Alongside the investigation of novel printing protocols, proof-of-concepts for multiplex detection and distinguishing clinical patient samples from healthy donors were also presented. Overall, this thesis demonstrated the fabrication and optimization of microarray development shows promise in improving current biosensor designs, allowing for enhanced early-onset disease detection and monitoring. / Thesis / Master of Applied Science (MASc)

La présence de micro-organismes pathogènes dans les produits alimentaires représente un risque important de santé publique. La réglementation régit leur contrôle en imposant, dans la majorité des cas, la recherche d’une faible quantité de ces bactéries. Les méthodes de détection de référence sont simples à mettre en œuvre mais chronophages et nécessitent un temps d’analyse de plusieurs jours. Aussi, un des enjeux majeurs dans le domaine du contrôle alimentaire, est la mise au point de méthodes sensibles et rapides pour la détection d’un ou plusieurs pathogènes dans des matrices alimentaires. Ces nouvelles technologies ont pour but de réduire le nombre de toxi-infections alimentaires tout en augmentant la durée de commercialisation des produits et en limitant les impacts économiques négatifs pour les industries (longues périodes de stockage, rappels de lot, etc.).Dans ce contexte, nous nous sommes intéressés à la mise au point d’une méthode alternative aux méthodes de références, basée sur un biocapteur présentant une transduction de type résonance des plasmons de surface (SPR). Cette technologie présente de multiples avantages : simplicité de mise en œuvre, analyse en temps réel, absence de marquage, etc. Des preuves de concept de son utilisation, pour la détection de bactéries pathogènes ont été présentées dans la littérature, utilisant principalement des récepteurs de type anticorps.Au cours des travaux présentés dans cette thèse nous nous sommes intéressés à la détection de bactéries pathogènes alimentaires majeures en termes de prévalence ou de gravité de l’infection, qu’elles soient Gram positif ou Gram négatif. La production d’anticorps performants a également été optimisée pour obtenir des anticorps polyclonaux sensibles et spécifiques de plusieurs genres bactériens. Les cinétiques de croissance bactérienne ont été analysées par SPR afin d’identifier les principaux phénomènes impactant la détection. Des techniques en haute résolution ont permis une meilleure compréhension des événements se produisant à la surface du biocapteur. Ces études ont menés à l’obtention d’un système permettant la détection multiplexe d’un faible inoculum de bactéries pathogènes dans des matrices alimentaires (salade et poudre de lait infantile) en moins de 24h. / The presence of pathogenic micro-organisms in foodstuff is a major concern for health safety. Regulations impose, in most cases, the research of low levels of these bacteria. Although reference methods are simple, they are time-consuming and can require several days before obtaining results. This is why one of the major challenges in food hygiene science is the development of sensitive and rapid methods, for the detection of one or more pathogens. These new technologies aim to decrease the occurrence of foodborne infections, while improving both the shelf life of food products and industrial production costs (long storage times, recalls …).In this context, the development of an alternative method has been carried out in this work, using a biosensor with a transduction based on surface plasmon resonance (SPR). Such optical technology offers multiple benefits: ease-of-use, real-time analysis, label-free process… Proofs of concept for the use of this technology in basic conditions, for the detection of model bacteria, have been described in the literature, mostly using antibodies as receptors, but the full operation in "real" conditions encountered in industrial facilities still has to be tested and optimizedThis manuscript thus describes the detection of foodborne pathogenic bacteria playing a major role in terms of prevalence and/or severity of the caused infection, whether Gram positive or negative. The production of efficient antibodies was optimized, resulting in polyclonal antibodies sensitive and specific for multiple bacterial genera. Dynamics of bacterial growths were analysed by SPR in an effort to identify the main factors having an impact on the detection. High resolution SPR was used for a better understanding of reactions occurring at the surface of the biosensor. These studies lead to the development of a system capable of multiplex detection of low bacterial inoculum in food samples (lettuce and powdered infant formula) within less than 24 hours.