Polymeric materials have seen increasing use as microfluidic device substrates due to their low cost and the simplicity of templated fabrication procedures. I showed that poly(methyl methacrylate) (PMMA) microdevices could be enclosed in a boiling water bath, which allowed the seal to form more quickly than in conventional approaches, and enabled microchannels to remain hydrated throughout the bonding process. Microchip capillary electrophoresis (µ-CE) devices were fabricated using water-based enclosure, and a mixture of fluorescently labeled amino acids was separated in 30 s in these microchips. To create more robust capillary electrophoresis (CE) microdevices with improved separation performance, phase-changing sacrificial materials were developed for solvent bonding of polymer microchips. Devices were fabricated by filling channels in embossed PMMA with a heated liquid that formed a solid sacrificial layer at room temperature. The sacrificial material prevented the bonding solvent and softened PMMA from filling the channels. Once the sealing step was finished, the sacrificial layer was melted and removed, leaving enclosed microchannels. These solvent-welded devices withstood internal pressures >2,200 psi, and 300 CE runs were performed on a single microchip without any loss of separation performance. Furthermore, CE separations of peptides and amino acids were completed in ~10 s, with peak efficiencies of 43,000 theoretical plates. Electric field gradient focusing (EFGF), which uses a combination of pressure-driven flow and an electric field gradient to separate charged species according to their electrophoretic mobilities, was explored for protein analysis. Capillary-based EFGF devices were characterized; mixtures of four proteins were resolved, band focusing dynamics were studied, and analytes were enriched 10,000-fold. EFGF was miniaturized further to a microfluidic platform. Phase-changing sacrificial layers were employed to interface an electric field gradient enabling semi-permeable copolymer with microchannels. Because of decreased channel dimensions, EFGF microchips produced narrower bands and yielded threefold higher resolution compared with capillary-based devices. Beyond providing improved performance for polymer-based µ-CE and EFGF, the advances in microchip fabrication technology presented here should be applicable broadly in interfacing microfluidics with hydrogel structures, for example in sample pretreatment.

There is significant interest in reducing the frictional resistance that occurs along a surface in contact with a liquid. A novel approach to reducing the frictional resistance across a liquid-solid interface is the use of superhydrophobic surfaces. superhydrophobic surfaces are created in this work by the use of micro-fabrication techniques where systematic roughness is fabricated on a substrate surface which is subsequently treated with a hydrophobic coating. This work reports an experimental study of superhydrophobic surfaces used to reduce drag in both laminar and turbulent channel flows. In the laminar flow regime reductions in frictional resistance greater than 55% were measured in microchannels consisting of superhydrophobic walls. The reduction in frictional resistance for laminar flow in microchannels with superhydrophobic walls was shown to be dependent on the rib/cavity orientation, with greater reduction achieved when the ribs/cavities were aligned parallel with the direction of the flow. Also, the ratio of the cavity width to the combined rib/cavity pitch and the ratio of the combined rib/cavity pitch to the microchannel hydraulic diameter exercise influence on the frictional resistance. The condition when the flowing liquid was allowed to completely "wet" the cavities was also explored. Generalized expressions enabling prediction of the classical friction factor-Reynolds number product as a function of the relevant governing parameters were also developed. The influence of superhydrophobic surfaces in turbulent flow was explored in macrochannels using particle imaging velocimetry (PIV). For the turbulent flow regime the time-averaged velocity profiles revealed no discernible slip velocity at the superhydrophobic wall. However, the results did show that the superhydrophobic surfaces exhibits an influence on the streamwise and wall-normal turbulence intensities, the turbulent shear stress, the total shear stress distributions, and the turbulence production in the channel. From the total shear stress distributions in the channel the coefficient of friction at the channel walls was determined. The results showed that for the superhydrophobic surface with ribs and cavities oriented parallel to the flow direction a reduction in the coefficient of friction as high as 16% was achieved compared to a smooth wall channel. Superhydrophobic surfaces with ribs and cavities oriented transverse to the flow direction showed a modest increase in the coefficient of friction. Differential pressure measurements in the turbulent flow channel were also acquired and used to calculate the channel average friction factor.

The passive particle separation method of elasto-inertial microfluidics have greatpotential in the field of physics, biology and chemistry. The objective of thisdegree project was to understand particle behavior in curved microchannels fornon-Newtonian fluids. This in order to optimize the separation of 1 µm and 2 µmparticles where the end goal is to create an efficient sample preparation method fordiagnosing sepsis. Fluorescent beads were spiked into PEO solutions of differentconcentrations and used in microfluidic PDMS-glass chips with various radii toexamine the influence of curvature and elasticity as well as the flow rate. Theresult indicated an independence of both curvature and elasticity. Reynoldsnumber and Dean number are dependent on the flow rate which results in atrade-off between a high and low flow rate. A low Reynolds number is not enoughto create Dean vortices that can be used to separate particles while a highReynolds number creates strong Dean vortices that can obstruct the focusing. Later, microfluidic silicon-glass chips were used to separate 1 µm and 2 µm beads.The 2 µm particles were able to focus in two different PEO concentrations whereasthe 1 µm particles did not have time to focus entirely. This makes it possible toseparate 2 µm particles along with some 1 µm particles towards one outlet whileleaving another outlet with only 1 µm particles. This is a promising start butfurther optimization is required before being applied to real bacteria separation. / Den passiva partikelseparationsmetoden elastisk tröghetsmikrofluidik har storapotential inom fysik, biologi och kemi. Målet med examensarbetet var att förståpartiklars förflyttning i krökta mikrokanaler för icke-newtonska vätskor. Dettagjordes för att optimera separering av 1 µm och 2 µm partiklar där slutmålet är attskapa en effektiv provberedningsmetod för att diagnostisera sepsis. Fluorescerandepartiklar tillsatta i PEO-l¨osningar av olika koncentrationer anv¨andes imikrofluidiska PDMS-glas chip med olika radier för att undersöka inverkan avkrökning och elasticitet samt flödeshastigheten. Resultatet indikerade ettoberoende av både krökning och elasticitet. Reynolds nummer och Deans nummerär beroende av flödeshastigheten vilket resulterar i en avvägning mellan en hög ochlåg flödeshastighet. Ett lågt Reynolds nummer är inte tillräckligt för att skapaDean virvlar vilket kan utnyttjas för att separera partiklar medan ett högtReynolds nummer framkallar starka Dean virvlar vilket kan hindra fokuseringen. Sedan användes mikrofluidiska kisel-glas chip för att separera 1 µm and 2 µmpartiklar. 2 µm partiklarna lyckades fokusera i två olika PEO-koncentrationermedan partiklarna av 1 µm inte fokuserade fullt ut. Detta gör det möjligt attseparera 2 µm partiklar tillsammans med ett antal 1 µm partiklar mot ett utloppsamtidigt som ett annat utlopp endast innehåller 1 µm partiklar. Det är enlovande start men ytterligare optimering krävs innan det kan tillämpas på faktiskbakterieseparation.

<p>Pathogen detection via viscosity quantification in biological systems has long been an essential aspect of biomedical research. The importance of persistent testing of pathogens such as <em>V. cholerae</em> and HIV has consistently been recognized but limited in regions where systematic and financial resources are unavailable. Current methods require the samples be transported to research labs primarily in large cities or different countries. For consistent pathogen testing to be performed in remote areas, detection methods must be designed for portability with laboratory standards and simplicity for use without much technical background in place. </p> <p>Particle Diffusometry is a visualization method on the result of the amplification of pathogen by quantifying the Brownian motion of suspended particles in a solution. The amplification usually occurs in the specialized machine; then, the fluid sample gets inserted into the microfluidic chip for optical observation for Brownian motion. The technique has been used in particle sizing and measuring viscosity change in the biomolecular solution. In use with limitations, I present the improvements on the existing Particle Diffusometry technique to expand its use in broader biomedical applications.</p> <p>We address the portability of the technique. In the emerging and fast-growing mobile technology market, we have developed a smartphone-based portable platform capable of performing par quality tasks compared to traditional lab-based microscopy. We successfully measure the presence of <em>V. cholerae</em> as few as 6 cells/reaction, a waterborne pathogen, where its DNA is spiked into environmental water sources in just under 35 minutes. To further make the overall technology portable, we developed an on-chip amplification method accompanied by the portable heating unit. A mobile heating unit removes the need for the qPCR machine to amplify the biomolecular structure. Also, it opens the capability of on-chip amplification, further simplifying the steps needed to identify the pathogen in the source. We confirm the validity of the developed setup by measuring the presence of as low as 50 SARS-CoV-2 virus particles within 10% saliva. </p> <p>Addressing two main limitations of the existing Particle Diffusometry technique, improvements in the algorithm occur. First, we improve the algorithm to calculate diffusion coefficients even when the particles suspended in the sample are experiencing unified patterns, hence the flow, when recording is taking place. The improved algorithm correctly identified the diffusion coefficient within  margin of error using simulation and experimental verification for the sample under simple shear flow types, uniform, Couette, and Poiseuille. Second, we address the mismatch between the frame rate of the camera and the Brownian motion of particles at elevated temperatures. By configuring the correction equation for the frame mismatch behavior, we corrected the deviation of the diffusion coefficient in the range of 3E-13 to 3E-12 m²/s. Ultimately, we applied the improved flow algorithm to the elevated temperature simulation, showing the error propagation does not differ by the temperature; the percentage of error in computing the diffusion coefficient for the sample exhibiting flow only depends on the flow velocity. </p> <p>Applying these two improvements, we perform measurements on over-time viscosity change using the hydrogel formation. We characterize the hydrogel formation time using the diffusion gradient plane and variation of the initiator. By applying the addressed improvements on the real-time detection of HIV amplification on-chip, we further validate the applicative nature of the extended Particle Diffusometry technique. </p> <p>Real-time flow-adjusted Particle Diffusometry is, therefore, a feasible method for detecting viscosity changes in both chemical and biomolecular solutions in real-time. This approach opens up an alternative method for measuring biological amplification in real-time. The improvements further open the existing Particle Diffusometry technique to be widely used in the field involving rheology and pathogen detection not only in the traditional lab-based setting but also out in the field. </p>

This project aimed at exploring new hybrid materials to be used for acoustophoresis applications. Acoustophoresis can be used to manipulate particles inside a microfluidic channel by creating ultrasound standing waves within the channel [1]. This can be used for cell separation [2] or trapping of particles [3]. The intent of this project was to create materials for use in microfluidic channels that would be cheaper and easier to manufacture than those traditionally used, while still having adequate acoustic properties to allow for use in acoustopheresis. This was done by investigating whether the addition of glass-beads or glass-bubbles could increase the acoustic properties of an off-stoichiometry-thiol-enes (OSTE) based polymer. Hybrid samples with different volume fractions of glass-beads or glass-bubbles added to the OSTE polymer were manufactured and characterised according to their acoustic properties using the pulse-echo buffer-rod method. The acoustic properties measured were the density, attenuation, acoustic impedance and the reflection coefficient between water and the material. The addition of glass-beads was found to increase the acoustic impedance while the inverse was found for the addition of glass-bubbles. Both the addition of glass-beads and glass-bubbles were found to increase the attenuation. The hybrid material that was found to have the most suitable acoustic properties was OSTE/Glass-beads 40%, whose acoustic impedance had been increased ∼60% compared to pure OSTE. Consequently, the OSTE/Glass-beads 40% material was used to manufacture a microfluidic channel. A particle trapping experiment showed that the OSTE/Glass-beads 40% microfluidic channel was able to obtain bead trapping. This means that a standing wave was able to be generated within the channel and that it was strong enough to trap particles in the centre of the channel. However, evaluation of the particle trapping efficiency of the channel showed that it was not as effective as those using traditional materials. Therefore, future work is recommended to optimise a channel design for the OSTE/Glass-beads 40% material to increase the particle trapping efficiency. / I detta projekt undersöktes ett nytt hybridmaterial för användning i applikationer inom akustofores. Akustofores kan användas till att manipulera partiklar inuti mikrofluidkkanaler genom att generera ståendevågor i kanalen med hjälpav ultraljud [1]. Detta kan användas till cellseparation [2] eller till att fånga partiklar [3]. Målet i detta projekt var att skapa material som skulle bli billigare och möjliggöra enklare fabricering av kanalerna som används inom akustofores än de material som traditionellt används, med bibehållande av tillräckliga akustiskaegenskaper. Detta genomfördes genom att undersöka om tillsättning av glaspärlor eller glasbubblor kunde förbättra de akustiska egenskaperna av en off-stoichiometry-thiol-enes (OSTE) baserad polymer. Hybridprover gjorda på OSTE-polymeren med olika volymandelar av glaspärloroch glasbubblor tillverkades och kategoriserades med avseende på deras akustiska egenskaper med hjälp av pulseeko buffertstång metoden. De akustiska egenskaperna som uppmättes var densitet, attenuering, akustisk impedans och reflektions koefficienten mellan vatten och materialet. Resultatet av projektet visade att tillsättning av glaspärlor ökade den akustiska impedansen  i motsatts till glasbubblorna som visade sig minska den. Vidare visade det sig att både tillsättningen av glaspärlor och glasbubblor ökade attenueringen. Det hybridmaterial som visade sig ha de mest lämpliga akustiska egenskaperna var OSTE/glaspärlor med en 40% volymandel av glaspärlor. Den akustiska impedansen hade förhöjts med cirka 60% jämfört med vanlig OSTE. Därför valdes det hybrid-materialet till att tillverka en mikrofluidikkanal. Därefter genomfördes ett partikelfångstexperiment som visade att, OSTE/glaspärlor med en 40% volymandel av glaspärlor, kunde erhålla partikelfångst i kanalen. Detta innebär att en stående våg kunde genereras i kanalen och att den var tillräckligt stark för att kunna fånga partiklarna i mitten av kanalen. Däremot visade utvärdering av kanalens partikelfångsteffektivitet att den inte var lika effektiv som kanaler gjorda av traditionellt använda material. Därför rekommenderas framtida arbete till att designa en optimerad kanaldesign med OSTE/Glas-pärlor 40% materialets egenskaper i åtanke för att förhoppningsvis kunna öka partikelfångst effektivitet.

Microarray technology provides powerful tools in the field of biomedicalresearch because it can measure molecular interactions in a highly parallelfashion. It has uses in protein, DNA or cell research, in both discovery anddiagnostic applications. Microfluidics, on the other hand, provides thenecessary tools to rapidly transport and mix small volumes of sample to amicro-sensor area. Bridging these two technologies has the potential todevelop a miniaturized, automated and ease-of-use toolbox for biologicalanalysis. However, the integration of microfluidics with microarrays is notstraightforward, as if a robust and leak-tight seal between the microarray andthe microfluidic channels. Current sealing methods are either impractical,such as mechanical clamping, or not compatible with proteins, such as heat orplasma bonding or gluing. Moreover the former methods create a permanentseal that, once applied prevents the microfluidic structure to be removed later.This work focuses on developing a microfluidic add-ons ("Biosticker") that canbe robustly sealed with protein microarrays with maintained biologicalactivity, but at the same time easily removed to allow for multiple stickersapplied in a sequence or scanning of the microarray in a standard reader. Thefeatures of the novel Biostickers are made possible by the use ofOff-stoichiometry thiol-ene-epoxy (OSTEmer) polymers. In this thesis, wedesign and fabricate Biostickers for rapid integration with pre-spottedmicroarrays and experimentally verify how these micropatterned Biostickerscan be used to significantly facilitate multiplexed assays, by avoiding the useof beads. / Microarray-tekniken är ett kraftfullt verktyg inom biomedicinsk forskningeftersom den kan mäta miljontals molekylära interaktioner parallellt. Den haranvändningsområden i protein-, DNA- eller cellforskning, både i forskningoch diagnostik. Mikrofluidik, å andra sidan, ger de nödvändiga verktygen föratt snabbt transportera och blanda små provvolymer till en sensoryta. Genomatt kombinera dessa två teknologier finns potential att utveckla enminiatyriserad, automatiserad och lättanvänd verktygslåda för biologiskanalys. Emellertid är integrationen av mikrofluidik med mikroarrayer inteenkel, då ytorna är känsliga, kanalerna mycket små men tätningen måste varaperfekt. De vanligast förekommande förseglingsmetoder är antingenopraktiska, som mekaniskt tryck eller så är de inte kompatibla med proteiner,som t.ex. värme- eller plasmabondning. Dessutom syftar de flestaförseglingsmetoder mot att skapa en permanent försegling som vidanvändning förhindrar mikrofluidikstrukturer från att tas bort i ett senareskede, tex. vid avläsning i en skanner. Detta arbete fokuserar på att utvecklamikrostrukturerade plastartiklar ("Biosticker") innehållande kanaler ochkaviteter. Dessa Biosticker kan på ett robust och läckfritt sätt kansammanfogas med proteinmikroarrayer utan att påverka den biologiskaaktivitetet men samtidigt kunna avlägsnas för att tillåta flera Biostickersapplicerade i en sekvens eller scanning i en mikroarrayläsare. Dessafunktioner möjliggörs genom av så kallade icke-stökiometrska-tiol-ene-epoxipolymerer (OSTEmer) används som material. I den här avhandlingenutvecklas och tillverkas Biostickers för snabb integrering medproteinmikroarrayer. Det verifieras även experimentellt hur dessa Biostickerskan användas för att underlätta genomförandet av sk. multiplexadeprotinanalyser.

This work specifically aims to provide a fundamental framework, with some experimental validation, for understanding droplet emulsion dynamics in a microfluidic channel with an applied electric field. Electrification of fluids can result in several different modes of electrohydrodynamics (EHD). Several studies to date have provided theoretical, experimental, and numerical results for stationary droplet deformations and some flowing droplet configurations, but none have reported a method by which droplets of different diameters can be separated, binned and routed through the use of electric fields. It is therefore the goal of this work to fill that void and report a comprehensive understanding of how the electric field can affect flowing droplet dynamics. This work deals with two primary models used in electrohydrodynamics: the leaky dielectric model and the perfect dielectric model. The perfect dielectric model assumes that fluids with low conductivities do not react to any effects from the small amount of free charge they contain, and can be assumed as dielectrics, or electrical insulators. The leaky dielectric model suggests that even though the free charge is minimal in fluids with low conductivities, it is still is enough to affect droplet deformations. Finite element numerical results of stationary droplet deformations, implemented using the level set method, compare well both qualitatively (prolate/oblate and vortex directions), and quantitatively with results published by other researchers. Errors of less than 7.5% are found when comparing three-dimensional (3D) numerical results of this study to results predicted by the 3D leaky dielectric model, for a stationary high conductivity drop suspended in a slightly lower conductivity suspending medium. Droplet formations in a T-junction with no applied electric field are adequately predicted numerically using the level set finite element technique, as demonstrated by other researchers and verified in this study. For 3D models, droplet size is within 6%, and droplet production frequency is within 2.4% of experimental values found in the microfluidic Tjunction device. In order to reduce computational complexity, a larger scale model was solved first iii to obtain electrical potential distributions localized at the channel walls for the electrode placement configurations. Droplet deceleration and pinning is demonstrated, both experimentally and numerically, by applying steep gradients of electrical potential to the microchannel walls. As droplets flow over these electrical potential “steps,” they are pinned to the channel walls if the resulting electric forces are large enough to overcome the hydrodynamic forces. A balance between four dimensionless force ratios, the electric Euler number (Eue – ratio of inertial to electric forces), Mason number (M a – ratio of viscous to electric forces), electric pressure (P s – ratio of upstream pressure forces to electric forces), and the electric capillary number (Cae – ratio of electric to capillary forces) are used to quantify the magnitudes of each of these forces required to pin a droplet, and is consistent with a cubic dependency on the drop diameter. For larger drop diameters, effects of hydrodynamic forces become more prominent, and for smaller droplets, a greater electric forces is required due to the proximity of the droplet boundary with reference to the electrified channel wall. Droplet deceleration and pinning can be exploited to route droplets into different branches of a microfluidic T-junction. In addition, using steep electrical potential gradients placed strategically along a microchannel, droplets can even be passively binned by size into separate branches of the microfluidic device. These characteristics have been identified and demonstrated in this work.

The field of microfluidics has recently been gathering a lot of attention due to the enormous demand for devices that work in the micro scale. The problem facing many researchers and designers is the uncertainty in using macro scaled theory, as it seems in some situations they are incorrect. The general idea of this work was to decide whether or not the flow through micro diffusers and nozzles follow the same trends seen in macro scale theory. Four testing wafers were fabricated using PDMS soft lithography including 38 diffuser/nozzle channels a piece. Each nozzle and diffuser consisted of a throat dimension of 100µm x 50µm, leg lengths of 142µm, and half angles varying from 0o - 90o in increments of 5o. The flow speeds tested included throat Reynolds numbers of 8.9 -" 89 in increments of 8.9 using distilled water as the fluid. The static pressure difference was measured from the entrance to the exit of both the diffusers and the nozzles and the collected data was plotted against a fully attached macro theory as well as Idelchik's approximations. Data for diffusers and nozzles up to HA = 50o hints at the idea that the flow is neither separating nor creating a vena contracta. In this region, static pressure recovery within diffuser flow is observed as less than macro theory would predict and the losses that occur within a nozzle are also less than macro theory would predict. Approaching a 50o HA and beyond shows evidence of unstable separation and vena contracta formation. In general, it appears that there is a micro scaled phenomenon happening in which flow gains available energy when the flow area is increased and looses available energy when the flow area decreases. These new micro scaled phenomenon observations seem to lead to a larger and smaller magnitude of pressure loss respectively.

Quantum dots show great potential for use as spectral converters in solar cells, lighting applications, and biological imaging. These applications require precise control of quantum dot size to maximize performance. The quality, size, and fluorescence of quantum dots depend on parameters that are difficult to control using traditional batch synthesis processes. An alternative, high precision process was developed for the synthesis of cadmium-selenide quantum dots using a microfluidic reactor and fluorescence flow cell. The process required creating separate cadmium and selenium precursors that were then mixed in a nitrogen environment at 17°C. Using an NE-300® syringe pump, the solution was pumped through a microfluidic reactor submerged in a 240°C oil bath. The reactor then fed through a water quench bath at 25°C to terminate the nucleation and growth reaction. The fluorescence profiles of the quantum dot solutions were then characterized with an in-line fluorescence flow cell used in conjunction with an Ocean Optics® USB4000® spectrometer and a ThorLabs® LED UV light source. Flow rates through the reactor were varied from 0.05ml/min to 2ml/min. A central peak wavelength was registered in the fluorescence profiles for each flow rate. Monodisperse Cd-Se quantum dot solutions were synthesized across a broad spectrum of wavelengths ranging from 490nm to 620nm. An empirical relationship between flow rate and center wavelength was determined.

The purpose of this thesis project was to demonstrate the ability to utilize the capabilities of aptamers so that they may act as capture reagents for paper microfluidic devices. Several characterization experiments were conducted as a precursor before the final experimentation was performed. Paper characterization, manufacturing protocols for printing and heating, as well as 3D chip fabrication were all performed and analyzed. The results confirmed that the control of fluid through a 3D microfluidic device based in nitrocellulose is possible. For the biochemistry portion of this thesis report, antibodies and aptamers were chosen to react with IgE, an antibody that is present in high concentrations in the urine of patients diagnosed with respiratory distress. Antibody chips were successfully created as a baseline lateral flow assay for comparison to new aptamer detector reagents. The aptamer experiments were able to demonstrate that it is possible to utilize the capabilities of aptamers so that they may behave as capture reagents in paper microfluidic devices. Overall, the experiments performed were extremely supportive of the ability to develop the field of paper microfluidics with the use of aptamers so that patient populations across the globe can be more accurately and effectively diagnosed.