Development of an autonomous lab-on-a-chip system with ion separation and conductivity detection for river water quality monitoring

This thesis discusses the development of a lab on a chip (LOC) ion separation for river water quality monitoring using a capacitively coupled conductivity detector (C⁴D) with a novel baseline suppression technique.Our first interest was to be able to integrate such a detector in a LOC. Different designs (On-capillary design and on-chip design) have been evaluated for their feasibility and their performances. The most suitable design integrated the electrode close to the channel for an enhanced coupling while having the measurement electronics as close as possible to reduce noise. The final chip design used copper tracks from a printed circuit board (PCB) as electrodes, covered by a thin Polydimethylsiloxane (PDMS) layer to act as electrical insulation. The layer containing the channel was made using casting and bonded to the PCB using oxygen plasma. Flow experiments have been conduced to test this design as a detection cell for capacitively coupled contactless conductivity detection (C⁴D).The baseline signal from the system was reduced using a novel baseline suppression technique. Decrease in the background signal increased the dynamic range of the concentration to be measured before saturation occurs. The sensitivity of the detection system was also improved when using the baseline suppression technique. Use of high excitation voltages has proven to increase the sensitivity leading to an estimated limit of detection of 0.0715 μM for NaCl (0.0041 mg/L).The project also required the production of an autonomous system capable of operating for an extensive period of time without human intervention. Designing such a system involved the investigation of faults which can occur in autonomous system for the in-situ monitoring of water quality. Identification of possible faults (Bubble, pump failure, etc.) and detection methods have been investigated. In-depth details are given on the software and hardware architecture constituting this autonomous system and its controlling software

Design of a stark microchip

The possibility of constructing scalable quantum computation systems in the near future is quite intriguing. Emergent systems based on polar molecules as qubits and quantum gates are considered among the most promising candidates. Controlled loading of the microtraps in a quantum-state-selective manner is a critical precursor to the formation and manipulation of qubits. This thesis details a design of a microchip capable of controlling the motion of molecules in high-field-seeking and low-field-seeking quantum states. The design is based on an alternative type of a Stark decelerator/accelerator, the so-called type-B, in which the electrode separation distance changes along the beam axis while the electric field switching time remains constant. Monte-Carlo simulation method shows that a 2-cm long device consisting of 100 stages can decelerate HCN-like polar molecules, in a phase-stable manner, from 200 m/s to a near standstill in about 150 microseconds. The same device can be operated `in reverse' to accelerate stationary or slow moving molecules from microtraps. Two different types of geometries for alternating-gradient (AG) focusing of molecular motion are proposed. Comparison of the electric field distribution to the ideal harmonic field, as well as an analysis of the field magnitudes and gradients show that both geometries should be able to effectively decelerate or accelerate molecules while maintaining their transverse stability and focus. Finally, we propose a new technique for achieving longitudinal and transverse stability using only the accelerating fields. This new method is similar to the alternating phase focusing (APF) used in charged particle accelerators but applied to the case of polar molecules. We showed using 1D trajectory simulations that this technique is capable of decelerating molecules in a phase-stable manner, but were unable to confirm transverse focusing

Micron-Level Actuator for Thermal-Fluid Control in Microchannels

Effectiveness of an actuator is investigated for thermal-flow control in microchannels. First, simulations of a single actuator in a quiescent external medium are performed in order to study the parameters characterizing the synthetic jet flow from the actuator. For this purpose, a simplified, two-dimensional configuration is considered. The membrane motion is modeled in a realistic manner as a moving boundary in order to accurately compute the flow inside the actuator cavity. The geometric and actuation parameters of the actuator are investigated to define the effectiveness of the jet flow. The study is done initially at macro scales. Then, the flow in the Knudsen number range of less than 0.1 is modeled starting with a conventional compressible Navier-Stokes solver valid for continuum approach. Its boundary conditions, however, are modified to account for the slip velocity and the temperature jump boundary conditions encountered in micron-level devices. Compressibility effects are also taken into account and modeled through the compressible flow solver. The utility of synthetic jet actuators for manipulating fluid flows has been shown for mostly macro- and mini-scale applications. To the best of the author\u27s knowledge, there have been only a few studies on micro-sized synthetic jets; also they have only been modeled assuming continuum flow regime with no-slip at the walls. Therefore, several issues must still be addressed for micron-scale synthetic jets and also their applications to micron-level problems. Thus, as the second part of the study, a micron-level synthetic jet is proposed as a flow control device to manipulate the separated flow past a backward facing step in a microchannel. First, an uncontrolled flow past a backward facing step in a channel is computed. Then, a synthetic jet actuator is placed downstream of the step where the separation occurs. A large number of test cases have been analyzed. It is observed that the size of the separation bubble and its enstrophy are functions of the geometry of the actuator cavity and the membrane oscillation parameters. Considerable reduction in separation bubble size as well as in enstrophy is achieved using the actuator. Finally, a design for thermal management of a semiconductor device using the present actuator is introduced. For this purpose, a single microchip dissipating heat is placed in a two dimensional rectangular channel. Then, the different cavity and actuation parameters are considered in order to infer some characteristics of the effect of controlled synthetic jet thermal management. Using the actuator, a circulation region is generated on the top surface of the microelectronic chip. It is found that the fluctuating jet interacts with the channel flow and increases the convection rate by transferring linear momentum to the channel flow. It is seen from the results of the computations that the synthetic jets can be utilized effectively to control separation in internal flow applications and that they guarantee an efficient thermal management of microelectronic devices. Therefore, the synthetic jet actuator proves itself to be an effective device for thermal-fluid control applications where low-speed flows are encountered

Towards microwave based ion trap quantum technology

Scalability is a challenging yet key aspect required for large scale quantum computing and simulation using ions trapped in radio-frequency (rf) Paul traps. In this thesis 171Yb+ ions are used to demonstrate a magnetic field insensitive qubit which has a measured coherence time of 1.5 s, making it an ideal candidate to use for storing quantum information. A magnetic field sensitive qubit is also characterised which can be used for the implementation of multi-qubit gates using a potentially very scalable scheme based on microwaves in conjunction with a static magnetic field gradient instead of using lasers. However, the measured coherence time is limited by magnetic field fluctuations and will prohibit high fidelity gate operations from being performed. To address this issue, the preparation of a dressed-state qubit using a microwave based stimulated rapid adiabatic passage (STIRAP) pulse sequence will be presented. This qubit is protected against the noisy environment making it less sensitive to magnetic field fluctuations. The lifetime of this qubit is measured to demonstrate its suitability for storing quantum information. A powerful method for manipulating the dressed-state qubit will be presented and is used to measure a coherence time of the qubit of 500 ms which is two orders of magnitude longer compared to the magnetic field sensitive qubit. It will also be shown that our method allows for the implementation of arbitrary rotations of the dressed-state qubit on the Bloch sphere using only a single rf field. This substantially simplifies the experimental setup for single and multi-qubit gates. Furthermore, this thesis will present a experimental setup capable of successfully operating microfabricated surface ion traps. This setup is then used to operate and characterise the first two-dimensional (2D) lattice of ion traps on a microchip. A unique feature of the microfabrication technique used for this device is the extremely large voltage that can be applied which allows long ion lifetimes along with large secular frequencies to be measured, demonstrating the robustness of this device. Rudimentary shuttling between neighbouring lattice sites will be shown which could be used as part of a efficient scheme to load a large lattice of ions. One of the many applications of a 2D lattice of ions lies in the field of quantum simulations where many-body systems such as quantum magnetism, high temperature superconductivity, the fractional quantum hall effect and synthetic gauge fields can be simulated. It will be shown how making only minor modifications to the microchip the ion-ion separation can be reduced sufficiently to offer an exciting platform for the successful implementation of 2D quantum simulations. A theoretical investigation on the optimal 2D ion trap lattice geometry will also be presented with the aim to maximise the ratio of ion-ion coupling strength to decoherence from motional heating of the ions and to laser induced off-resonant coupling

Development of a microchip electrophoresis system for online monitoring of atmospheric aerosol composition

2011 Spring.Includes bibliographical references.Atmospheric aerosols are solid or liquid particles that remain suspended in the environment for an extended time because of their size. Due to their high number concentration, low mass concentration, unique size range, and high temporal and spatial variability, atmospheric aerosols represent a significant unknown in both environmental impact and human health. Despite the importance of aerosols, current instrumentation for monitoring their chemical composition is often limited by poor temporal resolution, inadequate detection limits, lack of chemical speciation, and/or high cost. To help address these shortcomings, microchip electrophoresis (MCE) has been introduced for the semi-continuous monitoring of water-soluble aerosol composition. The MCE instrument was coupled to a water condensation particle collector (growth tube), and the integrated system is termed Aerosol Chip Electrophoresis (ACE). ACE is capable of measuring particle composition with temporal resolution of 1 min and detection limits of ~100 ng m-3. This dissertation covers the development process of the prototype ACE instrument, including the novel separation chemistry, necessary modifications to traditional microfluidic devices, and the interface between the growth tube and the microchip

Theoretical and Experimental Development of Bipolar Based Fluorescence Detection for Microchip Electrophoresis

Abstract Methods for the separation and detection of reactive oxygen and nitrogen species (RNOS) at the cellular level can be useful tools for the study of the biochemical mechanisms of neurodegenerative diseases. Microchip electrophoresis (ME) is a promising analytical separation technique that can be used to separate these short-lived RNOS since it offers sub-minute analysis times, low sample volumes, and the ability for single cell analysis. Amperometric detection is one of the most popular detection methods for ME and has been used for the detection of RNOS and related antioxidants. In this thesis, a dual-channel/dual-parallel electrode system is developed to identify electroactive species based on their redox properties without the need for complicated data correction procedures. This new strategy was applied to distinguish nitrite from azide in a cell sample. Azide is a contaminant that is introduced by the filters used to remove cell debris. Microchip electrophoresis can also be coupled to fluorescence detection (FL) for the investigation of RNOS production in macrophage cells using different fluorescent dyes for specific RNOS that exhibit similar excitation and emission wavelengths. Using ME-FL, the effect of engineered carbon nanoparticles on ROS production by microglia and lung epithelial cells was investigated. In this dissertation, a novel detection method for ME was developed that takes advantage of both electrochemical and fluorescence detection. This method involves transforming an electrochemical signal to a fluorescence signal using a bipolar electrode. The new method was evaluated with two model reducible analytes using 2,7-dichlorodihydrofluorescein (DCFH2) as the fluorescence reporter. In addition, modeling of the ME-bipolar electrochemistry/ fluorescence experimental setup was performed using COMSOL Multiphysics. Programs were developed to generate bipolar cell voltammograms and to model the effect of the flow rate on the size of the fluorescence plug formed at the detector electrode. As a result of these studies, a bipolar fluorescence detection method was developed that was able to obtain low micromolar detection limits for reductive analytes. The method was further developed to obtain the bipolar fluorescence response without a potentiostat and with a simplified experimental setup. This development will be extended in the future to detect oxidizable analytes such as RNOS in cells. Additionally, chemiluminescence reporting can be used instead of fluorescence reporting to obtain better detection limits. Lastly, this system could be coupled to a miniaturized optical detection system to develop a portable microchip device capable of detecting electroactive species on-site

A passive portable microfluidic blood-plasma separator for simultaneous determination of direct and indirect ABO/Rh blood typing

The blood typing test is mandatory in any transfusion, organ transplant, and pregnancy situation. There is a lack of point-of-care (POC) blood typing that could perform both direct and indirect methods using a single droplet of whole blood. This study presents a new methodology combining a passive microfluidic blood–plasma separator (BPS) and a blood typing detector for the very first time, leading to a stand-alone microchip which is capable of determining the blood group from both direct and indirect methods simultaneously. The proposed design separates blood cells from plasma by applying hydrodynamic forces imposed on them, which overcomes the clogging issue and consequently maximizes the volume of the extracted plasma. An axial migration effect across the main channel is responsible for collecting the plasma in plasma collector channels. The BPS novel design approached 12% yield of plasma with 100% purity in approximately 10 minutes. The portable BPS was designed and fabricated to perform ABO/Rh blood tests based on the detection of agglutination in both antigens of RBCs (direct) and antibodies of plasma (indirect). The differences between agglutinated and non-agglutinated samples were distinguishable by the naked eye and also validated by particle analysis of microscopic pictures. The results of this passive BPS in ABO/Rh blood grouping verified the quality and quantity of the extracted plasma in practical applicationsPostprint (author's final draft

High-Performance Computing of Flow, Diffusion, and Hydrodynamic Dispersion in Random Sphere Packings

This thesis is dedicated to the study of mass transport processes (flow, diffusion, and hydrodynamic dispersion) in computer-generated random sphere packings. Periodic and confined packings of hard impermeable spheres were generated using Jodrey–Tory and Monte Carlo procedure-based algorithms, mass transport in the packing void space was simulated using the lattice Boltzmann and random walk particle tracking methods. Simulation codes written in C programming language using MPI library allowed an efficient use of the high-performance computing systems (supercomputers). The first part of this thesis investigates the influence of the cross-sectional geometry of the confined random sphere packings on the hydrodynamic dispersion. Packings with different values of porosity (interstitial void space fraction) generated in containers of circular, quadratic, rectangular, trapezoidal, and irregular (reconstructed) geometries were studied, and resulting pre-asymptotic and close-to-asymptotic hydrodynamic dispersion coefficients were analyzed. It was demonstrated i) a significant impact of the cross-sectional geometry and porosity on the hydrodynamic dispersion coefficients, and ii) reduction of the symmetry of the cross section results in longer times to reach close-to-asymptotic values and larger absolute values of the hydrodynamic dispersion coefficients. In case of reconstructed geometry, good agreement with experimental data was found. In the second part of this thesis i) length scales of heterogeneity persistent in unconfined and confined sphere packings were analyzed and correlated with a time behavior of the hydrodynamic dispersion coefficients; close-to-asymptotic values of the dispersion coefficients (expressed in terms of plate height) were successfully fitted to the generalized Giddings equation; ii) influence of the packing microstructural disorder on the effective diffusion and hydrodynamic dispersion coefficients was investigated and clear qualitative corellation with geometrical descriptors (which are based on Delaunay and Voronoi spatial tessellations) was demonstrated