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Even though most of the properties of optical fields, such as wavelength, polarization, wavefront curvature or angular spectrum, have been commonly manipulated in a variety of remote sensing procedures, controlling the degree of coherence of light did not find wide applications until recently. Since the emergence of optical coherence tomography, a growing number of scattering techniques have relied on temporal coherence gating which provides efficient target selectivity in a way achieved only by bulky short pulse measurements. The spatial counterpart of temporal coherence, however, has barely been exploited in sensing applications. This dissertation examines, in different scattering regimes, a variety of inverse scattering problems based on variable spatial coherence gating. Within the framework of the radiative transfer theory, this dissertation demonstrates that the short range correlation properties of a medium under test can be recovered by varying the size of the coherence volume of an illuminating beam. Nonetheless, the radiative transfer formalism does not account for long range correlations and current methods for retrieving the correlation function of the complex susceptibility require cumbersome cross-spectral density measurements. Instead, a variable coherence tomographic procedure is proposed where spatial coherence gating is used to probe the structural properties of single scattering media over an extended volume and with a very simple detection system. Enhanced backscattering is a coherent phenomenon that survives strong multiple scattering. The variable coherence tomography approach is extended in this context to diffusive media and it is demonstrated that specific photon trajectories can be selected in order to achieve depth-resolved sensing. Probing the scattering properties of shallow and deeper layers is of considerable interest in biological applications such as diagnosis of skin related diseases. The spatial coherence properties of an illuminating field can be manipulated over dimensions much larger than the wavelength thus providing a large effective sensing area. This is a practical advantage over many near-field microscopic techniques, which offer a spatial resolution beyond the classical diffraction limit but, at the expense of scanning a probe over a large area of a sample which is time consuming, and, sometimes, practically impossible. Taking advantage of the large field of view accessible when using the spatial coherence gating, this dissertation introduces the principle of variable coherence scattering microscopy. In this approach, a subwavelength resolution is achieved from simple far-zone intensity measurements by shaping the degree of spatial coherence of an evanescent field. Furthermore, tomographic techniques based on spatial coherence gating are especially attractive because they rely on simple detection schemes which, in principle, do not require any optical elements such as lenses. To demonstrate this capability, a correlated lensless imaging method is proposed and implemented, where both amplitude and phase information of an object are obtained by varying the degree of spatial coherence of the incident beam. Finally, it should be noted that the idea of using the spatial coherence properties of fields in a tomographic procedure is applicable to any type of electromagnetic radiation. Operating on principles of statistical optics, these sensing procedures can become alternatives for various target detection schemes, cutting-edge microscopies or x-ray imaging methods.

Healthcare-associated infections present an escalating worldwide issue, further intensified by the emergence of antimicrobial resistance and the spread of pathogens on surfaces. Current infection prevention methods have shown limited effectiveness, leading to several health issues, an overuse of antibiotics, and a continuous threat of surface recontamination. In response, extensive research has focused on bioinspired omniphobic smart coatings that effectively reduce the contact area available for pathogen attachment, achieved through an increase in surface roughness and apparent surface energy. This thesis introduces a new class of an omniphobic spray-coating, featuring hierarchical structured polydimethylsiloxane (PDMS) microparticles coated with gold nanoparticles, encompassing primary microscale (~0.23 𝜇m) and secondary nanoscale (~5 nm) buckyball and labyrinth wrinkles. This substrate-independent coating efficiently repels a wide range of liquids, including pathogens, even under harsh conditions like high temperatures, ultraviolet (UV) exposure, and abrasions. Repellency tests comparing coated and uncoated gloves revealed that uncoated gloves spread contamination to 50 secondary surfaces, while coated gloves transferred fewer bacteria and viruses to just three and two surfaces, respectively. The investigation extended to the coating's biocidal capabilities, incorporating gold nanoparticles functionalized with mercapto-silane to create a "Repel and Kill" coating. This process initiates chemisorption through thiol-gold bonding, allowing for the formation of diverse surface structures, including three-dimensional self-assembly, multilayers, and island structures. These modifications significantly enhance the roughness and hydrophobicity of the gold nanoparticles, amplifying their biocidal effectiveness. The wrinkled structure of PDMS contribute to repellency, while the functionalized gold nanoparticles play a crucial role in the antimicrobial property. This enhancement was evident in the antibacterial tests, which exhibited an immediate 99.90% reduction in bacterial adhesion for both MRSA and Pseudomonas aeruginosa (P. aeruginosa), followed by an additional 99.70% and 99.90% reduction in bacterial growth after 8 hours for MRSA and P. aeruginosa, respectively. Moreover, the coating's antiviral properties were confirmed, demonstrating a 98% reduction in the transfer of the bacterial virus Phi6. Recognizing the role of hospital fabrics as potential reservoirs for infection transmission, primarily due to their ability to sustain bacterial growth for extended periods, especially in the presence of bodily fluids, we took further steps to modify the wrinkled PDMS microparticles. This involved the incorporation of silver nanoparticles, capped with a positively charged ligand known as branched polyethyleneimine (bPEI). Additionally, we integrated a colorimetric sensor, giving rise to the "Repel, Kill, and Detect" smart coating. The transition of color from blue to green-yellow provided a tangible indicator of contamination detection based on the acidic mileu of the biofilms. To evaluate its realworld effectiveness, we conducted simulations of infection transmission in hospital environments, resulting in a remarkable reduction in pathogen adhesion from urine and feces by 99.88% and 99.79%, respectively, compared to uncoated fabrics. To further enhance the validation of our results, we employed a powerful deep learning network architecture, that determined whether the surfaces are contaminated or safe. In the face of evolving health challenges, this coating emerges as a resilient and adaptable solution, promising to enhance overall safety and alleviate the burden of infectious diseases. / Thesis / Doctor of Engineering (DEng) / The prolonged survival of pathogens on surfaces, significantly highlighted by the COVID-19 global pandemic, has intensified the urgency of addressing contamination on high-touch surfaces. Engineered surface coatings with repellent properties have emerged as a long-lasting and health-conscious solution for infection prevention and control. In this thesis, we introduce a new class of multifunctional engineered coatings featuring hierarchical structures adorned with biocidal nanoparticles and an integrated colorimetric sensor. We comprehensively investigate these coatings' multifunctional capabilities to repel, exterminate, and detect contaminants. Through specific characterization tests involving a wide range of pathogens, including viruses, bacteria, and fungi, within complex biological fluids like urine and feces, this research culminates in the development of surface coatings equipped with both antimicrobial and pathogen-sensing capabilities. In addition to advancing our understanding of surface hierarchy and chemical modifications for repellency and biocidal activity, this thesis yields insights into the dynamics of biofouling and pathogen transfer, with the overarching goal of reducing pathogen transmission via surfaces.

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Two main subjects, ellipsometry and computer screen photo-assisted techniques (CSPT), form the main line in this thesis. Ellipsometry is an optical technique based on the detection of polarization changes of light upon interaction with a sample. As most optical detection techniques it is non-intrusive and an additional advantage is its high surface sensitivity: thickness resolution in the order of pm can in principle be achieved. Therefore, ellipsometry is widely used as a technique for determination of optical constants and layer thickness for thin-layer structures. Lately ellipsometry has also been proposed for sensing applications, utilizing the detection of changes in the properties of thin layers. One application is described in this thesis concerning the detection of volatile organic solvents in gas phase using modified porous silicon layers, fabricated by electrochemical etching of silicon to create nm-sized pores. This greatly increases the surface area, promoting gas detection because the number of adsorption sites increases. Other applications of ellipsometry discussed in this thesis are based on combination with CSPT. CSPT is a way to exploit existing optical techniques for use in low-cost applications. In CSPT the computer screen itself is used as a (programmable) light source for optical measurements. For detection a web camera can be used and the whole measurement platform is formed by the computer. Since computers are available almost everywhere, this is a promising way to create optical measurement techniques for widespread use, for example in home-diagnostics. Since the only thing that needs to be added is a sample holder governing the physical or chemical process and directing the light, the cost can be kept very low. First, the use of CSPT for the measurement of fluorescence is described. Fluorescence is used in many detection applications, usually by chemically attaching a fluorescent marker molecule to a suitable species in the process and monitoring the fluorescent emission. The detection of fluorescence is shown to be possible using CSPT, first in a cuvette-based setup, then using a custom designed micro array. In the latter, polarizers were used for contrast enhancement, which in turn led to the implementation of an existing idea to test CSPT for ellipsometry measurements. In a first demonstration, involving thickness measurement of silicon dioxide on silicon, a thickness resolution in the order of nm was already achieved. After improvement of the system, gradients in protein layers could be detected, opening the door toward biosensor applications. Some further development will be needed to make the CSPT applications described here ready for the market, but the results so far are certainly promising.

Noble metal nanoparticles supporting localized surface plasmon resonances (LSPR) have been extensively investigated for label free detection of various biological and chemical interactions. When compared to other optical sensing techniques, LSPR sensors offer label-free detection of biomolecular interactions in localized sensing volume solutions. However, these sensors also suffer from a major disadvantage – LSPR sensors remain highly susceptible to interference because they respond to both solution refractive index change and non-specific binding as well as specific binding of the target analyte. These interactions can severely compromise the measurement of the target analyte in a complex unknown media and hence limit the applicability and impact of the sensor. In spite of the extensive amount of work done in this field, there has been a clear absence of efforts to make LSPR sensors immune to interfering effects. The work presented in this document investigates, both experimentally and numerically, dual- and tri-mode LSPR sensors that utilize the multiple surface plasmon modes of gold nanostructures to distinguish target analyte from interfering bulk and non-specific binding effects. Finally, a series of biosensing experiments are performed to examine various regeneration assays for LSPR sensors built on indium tin oxide coated glass substrate.

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La mise au point de capteurs optiques moyen infrarouge (MIR) pour la surveillance des polluants organiques dans l'environnement aquatique est actuellement un défi de grande importance. Les capteurs MIR basés sur la spectroscopie à ondes évanescentes sont des outils d'analyse prometteurs pour la détection et la quantification simultanées d'une variété de polluants tels que les composés hydrocarbonés. Les verres de chalcogénure sont particulièrement bien adaptés aux applications de détection en raison de leur large domaine de transparence (jusqu'à 10-16 µm en fonction de leur composition). Ainsi, des films minces de chalcogénure pour le développement de plates-formes optiques intégrées ont été synthétisés. Leur fonctionnalisation par des polymères afin d'augmenter la sensibilité des capteurs a également été réalisée. Parmi les compositions de verre (GeSe2)100-x(Sb2Se3)x, deux cibles en verre séléniure ont été choisies pour leurs propriétés optiques et physiques. Grâce à la spectroscopie de réflexion totale atténuée, des mesures ont été effectuées dans l'eau pour détecter les hydrocarbures aromatiques (benzène, toluène et les trois isomères du xylène) dans des concentrations comprises entre 250 ppb et 40 ppm. Des mesures de détection ont également été effectuées à l'aide d'eau de mer et d'eau souterraine. Pour augmenter leur sensibilité, l'utilisation de nanoparticules métalliques est l'une des solutions prometteuses basées sur l'absorption infrarouge améliorée en surface (SEIRA). Ainsi, des structures hybrides combinant nanoparticules d'or déposées sur des verres de chalcogénure ont été fabriquées et caractérisées. / The development of middle-infrared (MIR) sensors for organic pollutants monitoring in the aquatic environment is currently a challenge of great importance. The mid-infrared sensor based on evanescent wave spectroscopy is a promising analytical tool for simultaneous detection and quantification of a variety of pollutants such as hydrocarbon compounds. Chalcogenide glasses are particularly well adapted for sensing applications due to their wide domain of transparence (up to 10-16 µm depending on their composition). The aims of this study are to synthetize chalcogenide thin films for developing mid-infrared optical integrated platforms and perform their functionalization with polymers in order to increase the sensor sensitivity. Among (GeSe2)100-x(Sb2Se3)x glass compositions, two selenide glass targets were chosen for their optical and physical properties. Thanks to attenuated total reflection spectroscopy, measurements were performed in water to detect aromatic hydrocarbons (benzene, toluene and the three xylene isomers) in the concentrations range of 25 ppb to 10 ppm. Detection measurements have also been fulfilled using seawater and ground-water. To increase their sensitivity, the use of metallic nanoparticles is one of the promising solutions based on Surface Enhanced Infrared Absorption (SEIRA). Thus, hybrid structures combining gold nanoparticles/chalcogenide glass and waveguides were fabricated and characterized.

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