Test analysis & fault simulation of microfluidic systems

This work presents a design, simulation and test methodology for microfluidic systems, with particular focus on simulation for test. A Microfluidic Fault Simulator (MFS) has been created based around COMSOL which allows a fault-free system model to undergo fault injection and provide test measurements. A post MFS test analysis procedure is also described.A range of fault-free system simulations have been cross-validated to experimental work to gauge the accuracy of the fundamental simulation approach prior to further investigation and development of the simulation and test procedure.A generic mechanism, termed a fault block, has been developed to provide fault injection and a method of describing a low abstraction behavioural fault model within the system. This technique has allowed the creation of a fault library containing a range of different microfluidic fault conditions. Each of the fault models has been cross-validated to experimental conditions or published results to determine their accuracy.Two test methods, namely, impedance spectroscopy and Levich electro-chemical sensors have been investigated as general methods of microfluidic test, each of which has been shown to be sensitive to a multitude of fault. Each method has successfully been implemented within the simulation environment and each cross-validated by first-hand experimentation or published work.A test analysis procedure based around the Neyman-Pearson criterion has been developed to allow a probabilistic metric for each test applied for a given fault condition, providing a quantitive assessment of each test. These metrics are used to analyse the sensitivity of each test method, useful when determining which tests to employ in the final system. Furthermore, these probabilistic metrics may be combined to provide a fault coverage metric for the complete system.The complete MFS method has been applied to two system cases studies; a hydrodynamic “Y” channel and a flow cytometry system for prognosing head and neck cancer.Decision trees are trained based on the test measurement data and fault conditions as a means of classifying the systems fault condition state. The classification rules created by the decision trees may be displayed graphically or as a set of rules which can be loaded into test instrumentation. During the course of this research a high voltage power supply instrument has been developed to aid electro-osmotic experimentation and an impedance spectrometer to provide embedded test

Model-based Experimental Design in Electrochemistry

The following thesis applies an experimental design framework to investigate properties of electron transfer kinetics and homogeneous catalytic reactions. The approach is model-based and the classical Butler-Volmer description is chosen to describe the fundamental electrochemical reaction at a conductive interface. The methodology focuses on two significant design variables: the applied potential at the electrode and mass transport mode induced by physical arrangement. An important problem in electrochemistry is the recovery of model parameters from output current measurements. In this work, the identifiability function is proposed as a measure of correspondence between the parameters and output variable. Under diffusion-limit conditions, plain Monte Carlo optimization shows that the function is globally non-identifiable, or equivalently the correspondence is generally non-unique. However by selecting linear voltammetry as the applied potential, the primary parameters in the Butler-Volmer description are theoretically recovered from a single set of data. The result is accomplished via applications of Sobol ranking to reduce the parameter set and a sensitivity equation to inverse these parameters. The use of hydrodynamic tools for investigating electron transfer reactions is next considered. The work initially focuses on the rotating disk and its generalization - the rocking disk mechanism. A numerical framework is developed to analyze the latter, most notably the derivation of a Levich-like expression for the limiting current. The results are then used to compute corresponding identifiability functions for each of the above configurations. Potential effectiveness of each device in recovering kinetic parameters are straightforwardly evaluated by comparing the functional values. Furthermore, another hydrodynamic device - the rotating drum, which is highly suitable for viscous and resistive solvents, is theoretically analyzed. Combined with previous results, this rotating drum configuration shows promising potential as an alternative tool to traditional electrode arrangement. The final chapter illustrates the combination of modulated input signal and appro- priate mass transport regimes to express electro-catalytic effects. An AC voltammetry technique plays an important role in this approach and is discussed step-by-step from simple redox reaction to the complete EC′ catalytic mechanism. A general algorithm based on forward and inverse Fourier transform functions for extracting harmonic currents from the total current is presented. The catalytic effect is evaluated and compared for three cases: macro, micro electrodes under diffusion control condition and in micro fluidic environments. Experimental data are also included to support the simulated design results

Microsystems Integration Towards Point-of-Care Monitoring of Clozapine Treatment for Adherence, Efficacy, and Safety

Schizophrenia is a challenging and complex disorder with 30–50% of patients not responding to first line antipsychotic treatment. Clozapine is the only antipsychotic approved by the FDA for treatment-resistant schizophrenia and is the most effective antipsychotic medication currently available. Yet, clozapine remains underutilized because of the requirements for frequent invasive and burdensome monitoring to 1) titrate doses to achieve effective blood levels, as well as 2) monitor white blood cells on a weekly basis for the first six months due to risk of agranulocytosis, a rare but potentially fatal side effect of clozapine. These blood draws, and the time lag in receiving reports from central labs, can add several more visits to the caregivers' treatment plan, which may not be feasible for the patient nor the treatment team. This contributes to a very low prescription rate for clozapine, making it one of the most underutilized evidence-based treatments in the field of mental health. The objective of this work is to progress toward a point-of-care approach to monitor both white blood cells and clozapine within a clinical setting. This would significantly lower the burden associated with clozapine treatment by allowing both tests to be performed rapidly during a single doctor's office visit or at the pharmacy. Specifically, I have developed and studied novel clozapine detection schemes based on electrochemical signal amplification in chitosan-based films. Moreover, I have investigated impedance cytometry coupled with hydrodynamic focusing and osmotic lysis to provide label- and reagent-free differential white blood cell counting capabilities. Finally, I have integrated the components in a microsystem capable of concurrent sensing of both biomarkers in whole blood samples. This proof-of-concept device lays the foundation for a fully integrated and automated lab-on-a-chip for point-of-care or even at-home testing to ensure treatment adherence, efficacy, and safety. This will allow for broader use of clozapine by increasing convenience to patients as well as medical professionals, thus improving the lives of people affected by schizophrenia through personalized medicine

Towards electrochemical diagnostics of biochemical free radical species in aqueous microliter volumes

Reactive oxygen species (ROS) are free radicals often implicated in disease states. In probing related enzyme processes, reactant consumption must be minimized. Levitated drops show potential as microreactors where radicals are present as reactants or products. Solid/liquid interfaces are absent or minimized, avoiding adsorption and interfacial reaction of conventional microfluidics. Probing small volumes electrochemically requires an integrated sensor with reference, counter-, and one or more working electrodes. Microfabrication allows production of planar gold sensor microelectrodes. A design that placed eight copies of the sensor on a single wafer maximized throughput and use of available substrate area. Titanium was found to be superior to chromium in corrosion resistance while providing adequate adhesion between gold and the polyimide-passivated silicon substrate. A lithographic process using image reversal with lift-off proved superior to etching in terms of line width range, allowing resolution of narrow electrodes (<25 μm) and wider conductive paths. Photosensitive polyimide proved capable of insulating non-electroactive sensor regions, prevented the occurrence of metal delamination encountered in previous electrode designs, as well as defining active electrode areas. Laser milling detached individual electrodes from the wafer and shaped the tip for piercing the levitated drop. The resulting three-electrode sensor with microdisk gold working electrode of radius 19 μm was characterized using ferrocenemethanol in aqueous buffer. Using cyclic voltammetry, the electrochemically active surface area was estimated by combining a recessed microdisk electrode model with the Randles-Sevcik equation. Computer-controlled ballistic introduction of reactant droplets into a levitated drop was developed. Chronoamperometric measurements of ferrocyanide with the microfabricated electrode demonstrated the electrochemical monitoring of reactions in a levitated drop, as well as the feasibility of adding reactants ballistically to the drop. Although concentration increases with time due to drop evaporation, it was found to be predictable with a linear evaporation model. Comparison of diffusion-limited currents in pendant and levitated drops shows that convection arising from acoustic levitation causes an enhancement of diffusion-limited current on the order of 16%. The study of ROS-mediated processes requires a supply of the ROS under investigation. A flow system was designed to generate superoxide radical anion (O2 -) at near-neutral pH by rapid mixing of potassium superoxide dissolved in dimethyl sulfoxide by two- stage mixing with aqueous buffers. This system’s intended application is the delivery of O2 - to bacteria immobilized on filters for investigating attenuation by O2 - on Salmonella enterica serovar typhimurium. Measurements of flow rates and calculations of residence times indicate final aqueous O2 - concentrations up to 50 μM are possible. A spectrophotometric flow cell was devised to confirm the concentration of superoxide

Biosensors: 10th Anniversary Feature Papers

Biosensors are analytical devices used for the detection of a chemical substance, or analyte, which combines a biological component with a physicochemical detector. Detection and quantification are based on the measurement of the biological interactions. The biological element of a biosensor may consist of tissues, microorganisms, organelles, cell receptors, enzymes, antibodies and nucleic acids. These devices have been shown to have a wide range of applications in a vast array of fields of research, including environmental monitoring, food analysis, drug detection and health and clinical assessment, and even security and safety. The current Special Issue, “Biosensors: 10th Anniversary Feature Papers”, addresses the existing knowledge gaps and aids the advancement of biosensing applications, in the form of six peer-reviewed research and review papers, detailing the most recent and innovative developments of biosensors

Applications and Experiences of Quality Control

The rich palette of topics set out in this book provides a sufficiently broad overview of the developments in the field of quality control. By providing detailed information on various aspects of quality control, this book can serve as a basis for starting interdisciplinary cooperation, which has increasingly become an integral part of scientific and applied research

Microfluidics for Biosensing

There are 12 papers published with 8 research articles, 3 review articles and 1 perspective. The topics cover: Biomedical microfluidics Lab-on-a-chip Miniaturized systems for chemistry and life science (MicroTAS) Biosensor development and characteristics Imaging and other detection technologies Imaging and signal processing Point-of-care testing microdevices Food and water quality testing and control We hope this collection could promote the development of microfluidics and point-of-care testing (POCT) devices for biosensing

Implantable microelectrodes on soft substrate with nanostructured active surface for stimulation and recording of brain activities

Les prothèses neuronales implantables offrent de nos jours une réelle opportunité pour restaurer des fonctions perdues par des patients atteints de lésions cérébrales ou de la moelle épinière, en associant un canal non-musculaire au cerveau ce qui permet la connexion de machines au système nerveux. La fiabilité sur le long terme de ces dispositifs, se présentant sous la forme d'électrodes implantables, est un facteur crucial pour envisager des applications dans le domaine des interfaces cerveau-machine. Cependant, les électrodes actuelles pour l'enregistrement et la stimulation se détériorent en quelques mois voire quelques semaines. Ce défaut de fiabilité sur le long terme, principalement lié à une réaction chronique contre un corps étranger, est induit au départ par le traumatisme consécutif à l'insertion du dispositif et s'aggrave ensuite, durant les mouvements du cerveau, à cause des propriétés mécaniques inadaptées de l'électrode par rapport à celles du tissu. Au cours du temps, l'ensemble de ces facteurs inflammatoires conduit à l'encapsulation de l'électrode par une couche isolante de cellules réactives détériorant ainsi la qualité de l'interface entre le dispositif implanté et le tissu cérébral. Pour s'affranchir de ce phénomène, la biocompatibilité des matériaux et des procédés, ainsi que les propriétés mécaniques de l'électrode doivent être pris en considération. Durant cette thèse, nous avons abordé la question en développant un procédé de fabrication simple pour réaliser des dispositifs implantables souples en parylène. Les électrodes flexibles ainsi obtenues sont totalement biocompatibles et leur compliance est adaptée à celle du tissu cérébral ce qui limite fortement la réaction inflammatoire occasionnée par les mouvements du cerveau. Après avoir optimisé le procédé de fabrication, nous avons focalisé notre étude sur les performances du dispositif et sa stabilité. L'utilisation d'une grande densité d'électrodes micrométriques, avec un diamètre de 10 à 50 µm, permet de localiser les zones d'enregistrement en rendant possible, par exemple, la conversion d'un ensemble de signaux électrophysiologiques en une commande de mouvement. En contrepartie, la réduction de la taille des électrodes conduit à une augmentation de l'impédance ce qui dégrade la qualité d'enregistrement des signaux. Ici, un polymère conducteur organique, le poly(3,4-ethylenedioxythiophene), PEDOT, a été utilisé pour améliorer les caractéristiques électriques d'enregistrement d'électrodes de petites dimensions. Le PEDOT a été déposé sur la surface des électrodes par électrochimie avec une grande reproductibilité. Des dépôts homogènes avec des conductivités électriques très élevées ont été obtenus en utilisant différents procédés électrochimiques. Grâce à l'augmentation du rapport surface/volume induit par la présence de la couche de PEDOT, une diminution significative de l'impédance de l'électrode (jusqu'à 3 ordres de grandeur) a été obtenue sur une large plage de fréquences. De tests de vieillissement thermique accéléré ont également été effectués sans influence notable sur les propriétés électriques démontrant ainsi la stabilité de la couche de PEDOT durant plusieurs mois. Les dispositifs ainsi obtenus, fabriqués en parylène avec un dépôt de PEDOT sur la surface active des électrodes, ont été testés in vitro et in vivo sur des cerveaux de souris. Un meilleur rapport signal sur bruit a été mesuré durant des enregistrements neuronaux en comparaison avec des résultats obtenus avec des électrodes commerciales. En conclusion, la technologie décrite ici, associant stabilité sur le long terme et faible impédance, a permis d'obtenir des électrodes implantables parfaitement adaptées pour le développement d'interfaces neuronales chroniques.Implantable neural prosthetics devices offer, nowadays, a promising opportunity for the restoration of lost functions in patients affected by brain or spinal cord injury, by providing the brain with a non-muscular channel able to link machines to the nervous system. The long term reliability of these devices constituted by implantable electrodes has emerged as a crucial factor in view of the application in the "brain-machine interface" domain. However, current electrodes for recording or stimulation still fail within months or even weeks. This lack of long-term reliability, mainly related to the chronic foreign body reaction, is induced, at the beginning, by insertion trauma, and then exacerbated as a result of mechanical mismatch between the electrode and the tissue during brain motion. All these inflammatory factors lead, over the time, to the encapsulation of the electrode by an insulating layer of reactive cells thus impacting the quality of the interface between the implanted device and the brain tissue. To overcome this phenomenon, both the biocompatibility of materials and processes, and the mechanical properties of the electrodes have to be considered. During this PhD, we have addressed both issues by developing a simple process to fabricate soft implantable devices fully made of parylene. The resulting flexible electrodes are fully biocompatible and more compliant with the brain tissue thus limiting the inflammatory reaction during brain motions. Once the fabrication process has been completed, our study has been focused on the device performances and stability. The use of high density micrometer electrodes with a diameter ranging from 10 to 50 µm, on one hand, provides more localized recordings and allows converting a series of electrophysiological signals into, for instance, a movement command. On the other hand, as the electrode dimensions decrease, the impedance increases affecting the quality of signal recordings. Here, an organic conductive polymer, the poly(3,4-ethylenedioxythiophene), PEDOT, has been used to improve the recording characteristics of small electrodes. PEDOT was deposited on electrode surfaces by electrochemical deposition with a high reproducibility. Homogeneous coatings with a high electrical conductivity were obtained using various electrochemical routes. Thanks to the increase of the surface to volume ratio provided by the PEDOT coating, a significant lowering of the electrode impedance (up to 3 orders of magnitude) has been obtained over a wide range of frequencies. Thermal accelerated ageing tests were also performed without any significant impact on the electrical properties demonstrating the stability of the PEDOT coatings over several months. The resulting devices, made of parylene with a PEDOT coating on the active surface of electrodes, have been tested in vitro and in vivo in mice brain. An improved signal to noise ratio during neural recording has been measured in comparison to results obtained with commercially available electrodes. In conclusion, the technology described here, combining long-term stability and low impedance, make these implantable electrodes suitable candidates for the development of chronic neural interfaces