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

Methods for Fabricating Printed Electronics with High Conductivity and High Resolution

Flexible and printable electronics are attractive techniques which are believed to be widespread and occupy huge market. However, low conductivity, nozzle clog because of the accumulation of nano-particles and relative high cost (expensive silver/copper nanoparticle inks) limit its appeal. In this thesis, two new effective and convenient methods of fabricating copper patterns with high conductivity and strong adhesion on flexible photopaper and polymer substrates (PET) are demonstrated, solving all those problems. Functional photopaper and PET substrate was prepared with inkjet printing of a palladium salt solution and hyperthermal hydrogen induced cross-linking (HHIC) polyelectrolytes onto its surface respectively, followed by electroless deposition of copper, creating high quality flexible copper patterns on different substrates. The developed technique was successfully applied for fabricating functional flexible circuits such as radio frequency identification devices (RFID) antenna, micro-inductive coil and complex circuit board

Cell-Free Artificial Photosynthesis System

The objective of this research is to create a cell-free artificial platform for harvesting light energy and transforming the energy to organic compounds. In order to achieve this objective, we took the approach of mimicking the photosynthetic processes of a plant leaf and integrating them into a compact system using microfabrication technology. Photosynthesis consists of two parts: light reaction and dark reaction. During the light reaction, light energy is transformed to chemical energy in ATP that is a biological energy source, while during the dark reaction. Carbon dioxide is absorbed and used to synthesize organic compounds such as glucose and fructose. Many scientists had tried to realize artificial photosynthesis for energy harvesting for decades. However, most of the previous systems were simply based on light reaction and produced less desirable energy sources, such as explosive hydrogen gas and unstable electricity. Other works had been reported that combined both light and dark reactions to produce useful organic compounds, but they were all based on utilizing living cells that were difficult to maintain and were not reusable. We developed a cell-free artificial platform conducting both light and dark reactions. To the best of our knowledge, such a device had not been reported so far. This device was able to harvest light energy and transform the energy to organic compounds, mimicking a plant leaf. We envision integrating the "artificial leaves" to create a compact energy harvesting system with a promising efficiency. In order to create an artificial photosynthesis device, we had come up with four specific parts as follows. Part 1: Light reaction was realized in a microfluidic platform that consists of two fluid chambers separated by a planar membrane with embedded proteins that convert light energy into ATP. Four different materials were investigated as potential membrane materials and the optimal (most stable) material was identified through impedance spectroscopy. Since these membrane materials were very soft, it was challenging to integrate them in a microfluidic platform. Diverse support materials and fabrication techniques were investigated to identify the optimal fabrication process. Once the best membrane material was identified and a microfluidic platform was constructed, we would have light-converting proteins embedded in the membrane followed by the evaluation its light reaction performance. Part 2: Dark reaction was realized in another microfluidic platform porous PDMS cubes as gas-liquid interface media. We used porous PDMS as a gas-liquid interface between microfluidic channels to create a "one-way" diffusion path for carbon dioxide. The CO2 transport was evaluated based on pH change and successful CO2 transport would produce precursors (C3 compounds) for glucose production. Part 3: Glucose synthesis and storage unit was developed by mimicking sponge mesophyll found in a leaf (dicotyledons leaf). Chitosan porous structures with interconnected pores were used for this purpose and they were fabricated by lyophilization after casting or 3D printing. Part 4: The circuits for an integrated light reaction platform was designed and simulated. The digital encode/decode of microchip array was simulated. A high-resolution, low-speed analog-to-digital converter was also designed and simulated for ion channel monitoring purpose. While carrying out this research, the following scientific contributions were also made. First, electrochemical property database of planar membranes made of different biomaterials were established. Second, a novel gas-liquid interface was developed for microfluidic platforms using porous PDMS and its performance was thoroughly investigated by on-chip pH measurement. Third, during the study on 3D printing of chitosan porous structure, a mathematical model was established for identifying optimal operational parameters for printing non-Newtonian fluids with a pneumatic printer. This research brought together expertise in advanced manufacturing (MEMS and additive manufacturing), biochemistry and biomaterials, and system control and integration. We envisioned integrating the "artificial leaves" to create a compact energy harvesting system with high efficiency.Ph.D., Mechanical Engineering and Mechanics -- Drexel University, 201

Ion conduction characteristics in small diameter carbon nanotubes and their similarities to biological nanochannels

In this study, we designed a series of experiments to determine the factors governing ion permeation through individual carbon nanotubes (CNTs) less than 1.5 nm in diameter and 20 µm in length. We then rationalize the experimental results by using a model, which is drawn from previous literature on protein ion channels and is centered around a simplified version of the Gouy-Chapman theory of electrical double layer. Lastly, we experimentally demonstrate and discuss the general similarities in ion permeation characteristics between CNTs and biological ion-selective pores. The role of many potential factors influencing the ion transport is assessed by taking two experimental approaches: (1) studying the effect of electrolyte concentration and composition on channel conductance and reversal potential, and (2) examining a second type of nanochannel as a parallel ion conduction pathway within the same device architecture and measurement set-up, which we refer to as leakage devices. This helps to differentiate the effect of CNT on ionic transport from any other possible source. Taken together, these two experimental methods provide strong evidence that the electrostatic potential arising from ionized carboxyl groups at the nanopore entrance has a significant effect on ionic permeation in a manner consistent with a simple electrostatic mechanism

Signal Enhancement Strategies in Classical Electrochemiluminescence Techniques for Modern Biosensing

With the ascent of IT, and since Ashton has invented the term Internet of Things (IoT) in 1999, this future idea of connected machines that can do tasks and perform decision-control cycles without human input has become more and more attractive and is today an established future scenario. Obviously, in an IoT, “sensors for everything” are one crucial corner stone of its existence and Analytical chemistry can and must deliver them. While many challenges towards a functioning IoT remain, we are on the verge of its beginning. This can be also seen with “Analytics 4.0” in research and on the market, tending to more IT-connected, portable, easier-controllable and integrated solutions. The entrance of mobility in the health sector or Point-of-Care (POC) diagnostics trends are alike influencing biosensing. Whether in mobile solutions or lab- and clinical environments, versatile, powerful and easy-to-adapt detection strategies like Electrochemiluminescence (ECL) are an attractive option. The ECL molecules [Ru(bpy)3]2+ and luminol represent the most prominent and most abundantly investigated luminophores for ECL since Bard’s accomplishment to make ECL a well-known technique. Because both are also two of the most efficient ECL emitters that can be well-handled in bioanalysis, and are available on the market, they are still today frequently used in research and also commercial applications. To cope with current benchmarks of sensitive detection, however a combination with a certain signal enhancement strategy is recommended. Several different routes can here be employed and one option is dendrimers. PAMAM dendrimers can function as ECL coreactant in [Ru(bpy)3]2+-ECL via their amino groups and at the same time expose primary amino groups as possible bioconjugation elements. Exploring this multi-functionality of the dendrimers was investigated here. This was done on a model system employing PAMAM dendrimers with [Ru(bpy)3]2+-ECL together with biotin/streptavidin as biorecognition element and analyte, respectively. The dendrimer’s bi-functionality was successfully proven and a joint-role of a biorecognition element and a possible reporter function suggests an optimum application in homogeneous assays. A different toolset for ECL signal enhancement is offered by liposomes. Numerous signaling molecules can be encapsulated inside the inner cavity of these synthetic vesicles, while they provide protection from the environment and connection-functionality to probes via lipids and surface groups on the outside. That application was here explored, together with a newly synthesized luminol derivative obtained by a simple synthesis route from commercial starting materials and exhibiting a four times increased ECL efficiency versus standard luminol. That was necessary as a liposome enhancement was denied for the standard luminol through its poor aqueous solubility. The new m-carboxy luminol considerably improved this feature which allowed its own encapsulation in liposomes. The superior signal generation with this dual system was proven in a model sandwich hybridization assay which yielded a 150-times better detection performance than the equal fluorescence-based assay while being almost zero affected through matrices like serum, soil or river water. As such the good performance of luminol ECL together with liposomes for highly sensitive detection applications was demonstrated. A further necessary element with liposomal amplification, are surfactants to set free the signaling molecules. However, this case depicts only one example of a multitude of applications of surfactants in bioassays and biochemical methods. Hence, surfactants are commonly present solution constituents which also have to be considered in general with ECL because they can influence the ECL signals positively or negatively. This was further investigated for luminol ECL by exploring the effect of 13 different surfactants on the luminol ECL efficiency on four different electrode materials. A deeper understanding of the distinct effects was obtained by looking into ECL emission behavior, electrochemical effects, the surfaces and Chemiluminescence effects. After all, the revelation of a complicated mechanism that involves many contributing factors and as such directs signal quenching or enhancement is an important finding for assay design. In this way, the selection of a suitable surfactant is possible to exploit maximum reachable signal efficiencies. A combination of signal enhancement tools like a better ECL molecule derivative, dendrimers, liposomes or surfactants has proven to boost the ECL performance considerably. A further means of signal enhancement is offered via miniaturization, which also makes the detection method better suited towards common application as liquid handling and easier automation are on hand. This can be used for single ECL assays or combinations of different ECL reagents in one system for multi-detection. Different strategies for the miniaturization of an ECL readout-capable system were investigated, taking requirements for [Ru(bpy)3]2+ and luminol as ECL reporters into account. This includes materials, electrochemical demands and simple design. Here, ITO electrodes – while advantageous for luminol ECL could not convince with their performance in [Ru(bpy)3]2+-ECL. Alternatively, laser scribed graphene electrodes have shown to be promising candidates for a future miniaturized system encompassing both, luminol and [Ru(bpy)3]2+ as ECL systems. Ultimately, the different signal amplifying strategies, investigated in this work that can be applied standalone or combined, offer a great toolset for state-of-the-art ECL detection applications in research and also for possible commercial applications

Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018

Bibliography of Lewis Research Center technical publications announced in 1989

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1989. All the publications were announced in the 1989 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses