There is a rising need for inline sensors for continuous and non-destructive monitoring of crops status. As growth in agricultural productivity stagnates, farmers are increasingly adopting soil-implanted sensors that allow them to optimize their yields. In existing literature, plant bio-impedance has been shown to change accordingly with various biotic and abiotic stress factors, and thereby may constitute a marker of interest. Yet, to date, there is no widespread adoption of bio-impedance for plant health monitoring due to the low sensitivity of planar electrodes. This thesis is dedicated to the development of a plant impedimetric biosensor that utilizes micro-needles electrodes for enhanced sensitivity. The micro-needles have been designed to pierce the upper waxy layer (cuticle) of plants to measure impedance from the underlying layers. Moreover, a micromolding process has been utilized to fabricate the micro-needles at scale without sacrificing fidelity. The molds were fabricated using dip-in laser lithography to benefit from the high resolution and flexibility of the technique. Standard metal sputtering processes were then used to confer conductivity onto the micro-needles. Several micro-needle aspect ratios and geometries were explored and adapted for use on Barley (Hordeum vulgare L,) and Date Palm (Phoenix dactylifera). In order to assess the performance of the sensors, the impedance of several plant specimens was monitored using the developed sensors alongside planar electrodes. The impedance measured by the sensors was lower than that reported by planar electrodes at low frequencies, indicating successful bypassing of the cuticle, as desired. No adverse effects were observed on the plant tissue post micro-needle attachment for seven days. Furthermore, a cyclical diurnal pattern of impedance was observed in both plants that was entrained by light. Finally, the micromolding technique developed in this thesis can help produce high- fidelity 3D electrodes for bio-impedance monitoring. Once the mold is fabricated, the electrodes can be produced at scale without the need of clean-room equipment. Furthermore, the fabricated sensors can monitor bio-impedance of plant specimens for extended durations of time and may offer a platform that can be functionalized to selectively quantify specific phytohormones of interest.

No description available.

abstract: Biosensors aiming at detection of target analytes, such as proteins, microbes, virus, and toxins, are widely needed for various applications including detection of chemical and biological warfare (CBW) agents, biomedicine, environmental monitoring, and drug screening. Surface Plasmon Resonance (SPR), as a surface-sensitive analytical tool, can very sensitively respond to minute changes of refractive index occurring adjacent to a metal film, offering detection limits up to a few ppt (pg/mL). Through SPR, the process of protein adsorption may be monitored in real-time, and transduced into an SPR angle shift. This unique technique bypasses the time-consuming, labor-intensive labeling processes, such as radioisotope and fluorescence labeling. More importantly, the method avoids the modification of the biomarker’s characteristics and behaviors by labeling that often occurs in traditional biosensors. While many transducers, including SPR, offer high sensitivity, selectivity is determined by the bio-receptors. In traditional biosensors, the selectivity is provided by bio-receptors possessing highly specific binding affinity to capture target analytes, yet their use in biosensors are often limited by their relatively-weak binding affinity with analyte, non-specific adsorption, need for optimization conditions, low reproducibility, and difficulties integrating onto the surface of transducers. In order to circumvent the use of bio-receptors, the competitive adsorption of proteins, termed the Vroman effect, is utilized in this work. The Vroman effect was first reported by Vroman and Adams in 1969. The competitive adsorption targeted here occurs among different proteins competing to adsorb to a surface, when more than one type of protein is present. When lower-affinity proteins are adsorbed on the surface first, they can be displaced by higher-affinity proteins arriving at the surface at a later point in time. Moreover, only low-affinity proteins can be displaced by high-affinity proteins, typically possessing higher molecular weight, yet the reverse sequence does not occur. The SPR biosensor based on competitive adsorption is successfully demonstrated to detect fibrinogen and thyroglobulin (Tg) in undiluted human serum and copper ions in drinking water through the denatured albumin. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2015

Au cours des dernières années, la recherche dans le domaine des bio-capteurs optiques sans marquage a connu une croissance rapide du fait de la nécessité de développer des méthodes toujours plus performantes pour la détection et la mesure de faibles concentrations de molécules spécifiques dans divers domaines. Parmi les différentes méthodes optiques existantes, les cristaux photoniques (CP) offrent une alternative prometteuse du fait de leur sensibilité. D’autre part, le diamant, utilisé comme matériau pour la réalisation de ces dispositifs offre de bonnes propriétés optiques et la possibilité de réaliser une fonctionnalisation de surface efficace facilement. Dans ce contexte, cette thèse propose un nouveau design de bio-capteur optique à cristaux photonique bi-dimensionnel en diamant, fonctionnant à des longueurs d'onde proche de 800 nm.Une géométrie originale de trous d'air circulaires organisés selon une maille carrée a été choisie pour maximiser la sensibilité du bio-capteur à des changements d'indice de réfraction en leur surface. Il a été démontré analytiquement que les modes à faible vitesse de groupe avaient une plus grande sensibilité à ces changements. Des méthodes numériques ont permis de préciser les paramètres géométriques optimaux du CP. Le design proposé est basé sur la mesure de décalage angulaire dans le spectre en réflexion d'un mode lent résonant du CP quand celui-ci est éclairé par une lumière monochromatique.Des films de diamant polycristallin de quelques centaines de nanomètres à quelques micromètres d’épaisseur ont été déposés sur différents substrats. L’ensemble des procédés technologiques nécessaires à la réalisation des CP et spécifiques aux films de diamant polycristallin ont été développés ou optimisés, comme, entre autre, un procédé de lissage obtenu par gravure plasma, un procédé de transfert de films de diamant sur un autre substrat par collage, un procédé d’amincissement des films de diamant et la fabrication des CP par lithographie électronique et gravure plasma.Les échantillons réalisés dans la salle blanche du C2N ont été mesurés optiquement et les hypothèses théoriques concernant les performances du capteur ont étés validées. Un mode avec une vitesse de groupe c/100 à une longueur d'onde de 800 nm a été mesuré et la sensibilité correspondant a cette structure a été estimée à 500 degrés par unité d'indice de réfraction (°/RIU), une valeur supérieure d’un ordre de grandeur à celles rencontrées couramment dans les capteurs à CP bidimensionnels. Ces résultats représentent un premier pas vers un biocapteur hautement sensible, comprenant une fonctionnalisation de surface du diamant pour une reconnaissance de cible spécifique. / Over the last years, the research on the label-free biosensor topic has experienced a very rapid growth because of the need to develop high-performing methods to detect and measure low concentrations of specific molecules in various fields. Among all the methods proposed, photonic crystals (PhC) structures offers a good alternative due to their sensitivity. Moreover, the use of diamond as material make the proposed device more attractive due to its optical properties, high chemical stability and efficiency of surface functionalization. In this context, this PhD thesis propose a new design of optical bio-sensor based on diamond two-dimensional photonic crystals, working at the wavelength near 800 nm.An original geometry of circular air holes arranged in squared lattice was chosen in order to maximize the sensitivity of such photonic structures to refractive index changes on their surface. It was analytically proven that modes with low group velocity are more sensitive to these variations. Numerical methods gave the necessary information to determine the optimal geometrical parameters of the PhC. The proposed design is based on measuring the shift of the angular reflectivity of a low group velocity guided mode resonance (GMR) PhC when probed with a single frequency light.Polycrystalline diamond films were grown on two different substrates, with thicknesses ranging from a few hundreds of nanometers to several micrometers. The technological processes required for the realization of PhC on polycrustalline diamond were developed or optimized, such as surface planarization by inductively coupled plasma (ICP) dry etching, diamond film transfer onto new substrate by wafer bonding process, diamond films thinning and surface patterning with PhC using Electronic Beam Lithography (EBL) and ICP methods.The samples realized in clean-room facilities were optically measured and the theoretical assumptions were validated. A GMR with a c/100 group velocity at a wavelength of 800 nm was measured and its sensitivity is estimated to be in the order of 500 degrees/ refractive index unit (°/RIU), a value that is one order of magnitude higher than the typical values encountered for sensors based on 2D PhC. These results represents a first step towards a highly sensitive bio-sensor, including a diamond surface functionalization for specific target recognition.

III-nitride nanostructures have generated tremendous scientific and technological interests in studying and engineering their low dimensional physics phenomena. Among these, 2D planar, free standing III-nitride nanomembranes are unrivalled in their scalability for high yield manufacture and can be mechanically manipulated. Due to the increase in their surface to volume ratio and the manifestation of quantum phenomena, these nanomembranes acquire unique physical properties. Furthermore, III-nitride membranes are chemically stable and biocompatible. Finally, nanomembranes are highly flexible and can follow curvilinear surfaces present in biological systems. However, being free-standing, requires especially new techniques for handling nanometers or micrometers thick membrane devices. Furthermore, effectively transferring these membrane devices to other substrates is not a direct process which requires the use of photoresists, solvents and/or elastomers. Finally, as the membranes are transferred, they need to be properly attached for subsequent device fabrications, which often includes spin coating and rinsing steps. These engineering complications have impeded the development of novel devices based on III-nitride membranes. In this thesis, we demonstrate the versatility of III-nitride membranes where we develop a thermal bio-sensor nanomembrane and solar energy photo-anode membrane. First, we present a novel preparation technique of nanomembranes with new characteristics; having no threading dislocation cores. We then perform optical characterization to reveal changes in their defect densities compared to the bulk crystal. We also study their mechanical properties where we successfully modulate their bandgap emission by 55 meV through various external compressive and tensile strain fields. Furthermore, we characterize the effect of phonon-boundary scattering on their thermal properties where we report a reduction of thermal conductivity from 130 to 9 W/mK. We employ these modifications to develop a thermal biosensor, which conformally gets attached to cells to measure their thermal properties. We also assess the statistical significance of our measurements to differentiate between different cell lines based on their measured thermal properties. Finally, we demonstrate the application of nanomembranes in solar-based water-splitting by merging them with nanowires to form nanowire membranes which are used to fabricate membrane photo-anodes. Finally, through optical, chemical and electrochemical measurements, we demonstrate their superior operations compared to typical fabrication techniques.

A fully integrated optical chem/bio sensor complete with integrated source, chemically sensitive waveguide, detector arrays, and associated signal processing electronics on a Si-CMOS chip is a challenging, but highly desirable goal. An evanescent-wave multimode interferometric sensing element is a sensitive method for sensing, which is easily integrated on Si-CMOS. This work is concerned with the design, analysis, and demonstration of a planar multimode interferometric chem/bio sensor that is compatible with the fabrication constraints of Si-CMOS. A 4000-micron-long interferometric that can be adapted for different agents by a particular sensing layer has been fabricated on silicon using silicon dioxide and silicon oxynitride. Hexaflouro-isopropanol substituted polynorbornene is the sensing layer. This sensor has also been fabricated on a Si-CMOS circuit with embedded photodetectors. A sensor on silicon was demonstrated with a minimum detectable index change of 2.0x10-6 using an accurate gas delivery system and a custom hermetic waveguide test chamber. A modal pattern analysis strategy has also been developed to extract the optimal SNR from the measured modal patterns. An understanding of the noise processes and spatial bandwidth effects has enabled an experimentally-based prediction of the index sensitivity of a fully integrated multimode chem/bio sensor on Si-CMOS at 9.2 x10-7. Theoretically, the sensitivity enhancement of high over low index sensing layers and transverse-magnetic over transverse electric modes is described. Also, the sensitivity enhancement of higher-order-transverse modes has been quantified. The wide-angle beam propagation method has been used to simulate the sensor. This simulation showed the relation between the modal pattern repetition period and sensor sensitivity. Further, the modal coupling properties of the multimode y-junction have been described. A second multimode y-junction has been designed to change the modal excitation under the SL, and thus the sensitivity. The chemo-optic response of the `substituted polynorbornene' polymer., hexaflouro-isopropanol substituted polynorbornene to methanol, water, iso-propanol, and benzene has been measured. Also, its thermo-optic response has been measured. Athermal interferometric chem/bio sensors have then been suggested.

abstract: Abnormally low or high blood iron levels are common health conditions worldwide and can seriously affect an individual’s overall well-being. A low-cost point-of-care technology that measures blood iron markers with a goal of both preventing and treating iron-related disorders represents a significant advancement in medical care delivery systems. Methods: A novel assay equipped with an accurate, storable, and robust dry sensor strip, as well as a smartphone mount and (iPhone) app is used to measure total iron in human serum. The sensor strip has a vertical flow design and is based on an optimized chemical reaction. The reaction strips iron ions from blood-transport proteins, reduces Fe(III) to Fe(II), and chelates Fe(II) with ferene, with the change indicated by a blue color on the strip. The smartphone mount is robust and controls the light source of the color reading App, which is calibrated to obtain output iron concentration results. The real serum samples are then used to assess iron concentrations from the new assay and validated through intra-laboratory and inter-laboratory experiments. The intra-laboratory validation uses an optimized iron detection assay with multi-well plate spectrophotometry. The inter-laboratory validation method is performed in a commercial testing facility (LabCorp). Results: The novel assay with the dry sensor strip and smartphone mount, and App is seen to be sensitive to iron detection with a dynamic range of 50 - 300 µg/dL, sensitivity of 0.00049 µg/dL, coefficient of variation (CV) of 10.5%, and an estimated detection limit of ~15 µg/dL These analytical specifications are useful for predicting iron deficiency and overloads. The optimized reference method has a sensitivity of 0.00093 µg/dL and CV of 2.2%. The correlation of serum iron concentrations (N=20) between the optimized reference method and the novel assay renders a slope of 0.95, and a regression coefficient of 0.98, suggesting that the new assay is accurate. Lastly, a spectrophotometric study of the iron detection reaction kinetics is seen to reveal the reaction order for iron and chelating agent. Conclusion: The new assay is able to provide accurate results in intra- and inter- laboratory validations and has promising features of both mobility and low-cost. / Dissertation/Thesis / Doctoral Dissertation Chemical Engineering 2020

No description available.

The continuous flow separation of magnetic particles from a mixture of particles could improve the performance of magnetic bead based assays but the formation of agglomerates limit the separation efficiency. Bead agglomerates are formed as a result of magnetic binding forces while the hydrodynamic fluid environment strongly influences their movement. The ability to predict the interaction between nearby beads will help to determine a threshold separation distance which will be recommended for use when obtaining measurement within a magnetic bead assay for a specified time interval. The introductory part of this thesis explored the development of a two dimensional numerical model in Matlab which predicts the trajectory pattern as well as magnetic induced velocities between a pair of super-paramagnetic beads suspended in water within a uniform field. The movement of a bead pair interacting due to both magnetic and hydrodynamic forces within a magnetophoretic system was recorded using an optical system; the beads' movements were compared with the simulated trajectories and gave a good agreement. The model was used to predict the shortest agglomeration time for a given separation distance which is of practical benefit to users of bead based assays. The concluding part of this thesis expanded the simulation into a three dimensional model to predict the interactions among three super-paramagnetic beads within a magnetophoretic system. In order to determine the height of the magnetic beads, a Huygens-Fresnel model was implemented in Matlab which was compared with off-focused diffracted images of the beads viewed under an optical system. A good comparison was obtained by comparing the simulated three-dimensional trajectories with experimental data.

As advances in thin films are made there is a parallel requirement to develop equipment capable of measuring their properties accurately and consistently. In addition there is a need to understand the parameters that are measured. Typical DPI measurements allow both the refractive index (related to density) and the thickness of the adsorbed layer to be calculated with relatively few assumptions, to a very high precision in real time. This thesis presents the research undertaken to develop multiple path length dual polarisation interferometry (MPL-DPI) and absorption enhanced dual polarisation interferometry (AE-DPI). In addition research is presented that can be used to improve the interpretation of the measured parameters for inhomogeneous films and uniaxial films. The new Interferometric technique MPL-DPI allows the thickness and refractive index of in situ and ex-situ coated ultra-thin films to be measured. The procedures and the mathematics required to calculate the properties of films have been described and the technique verified. The technique was demonstrated using films of PMMA, where good agreement was found with complementary techniques. Furthermore, some key features of MPL-DPI were demonstrated using the measurements of interfacially grafted acrylic acid. The absorption enhanced DPI uses the attenuation of the light within the waveguide, due to the light absorbing properties of a film on its surface. As the composition of a film changed, it was shown that the refractive index and extinction coefficients could be used to separate the mass of the components of the film that absorbed light, from the components of the film that did not. With the use of a semi-uniaxial model, the extra data from the attenuation in two polarisations was used to fit the extraordinary and ordinary extinction coefficients. The extraordinary and ordinary extinction coefficients were used to demonstrate that molecular orientation could be implied. The influence that an inhomogeneous film has on the measured thickness, refractive index and extinction coefficient fitted by homogeneous models were investigated. Formulas are presented to explain the thickness, refractive index and extinction coefficient of the measured film. A formula for the total mass per unit area that uses the refractive index was created to account for films that contain molecules of different refractive index increments (dn/dc's). To separate the mass of the individual molecular species from the total mass per unit area, formulas that use the extinction coefficient were derived so molecules that absorb light could be separated from those that do not. The mass calculated from the refractive index and the mass calculated from the extinction coefficient were also examined for uniaxial films. For uniaxial films both measures of the adsorbed mass were found to be relatively accurate and benefited from a partial cancellation of errors. The accuracy of the measurements made by dual polarisation interferometry technology is systematically examined throughout this thesis. Improvements in the calibration routines are suggested and a procedure for the identification and reduction of errors in the phase and contrast is demonstrated.