Planar digital nanoliter dispensing system based on thermocapillary actuation

We provide guidelines for the design and operation of a planar digital nanodispensing system based on thermocapillary actuation. Thin metallic microheaters embedded within a chemically patterned glass substrate are electronically activated to generate and control 2D surface temperature distributions which either arrest or trigger liquid flow and droplet formation on demand. This flow control is a consequence of the variation of a liquid’s surface tension with temperature, which is used to draw liquid toward cooler regions of the supporting substrate. A liquid sample consisting of several microliters is placed on a flat rectangular supply cell defined by chemical patterning. Thermocapillary switches are then activated to extract a slender fluid filament from the cell and to divide the filament into an array of droplets whose position and volume are digitally controlled. Experimental results for the power required to extract a filament and to divide it into two or more droplets as a function of geometric and operating parameters are in excellent agreement with hydrodynamic simulations. The capability to dispense ultralow volumes onto a 2D substrate extends the functionality of microfluidic devices based on thermocapillary actuation previously shown effective in routing and mixing nanoliter liquid samples on glass or silicon substrates

Demonstration of Automated DNA Assembly on a Digital Microfluidic Device

The rapid manufacturing of highly accurate synthetic DNA is crucial for its use as a molecular tool, the understanding and engineering of regulatory elements, protein engineering, genetic refactoring, engineered genetic networks and metabolic pathways, and whole-genome syntheses [1,2]. Recent efforts in the development of enzyme mediated oligonucleotide synthesis have shown much potential to benefit conventional DNA synthesis [3–5]. With its success in applications as chemical microreactors [6–10], biological assays [8–14], and clinical diagnostic tools [10,15–19], digital microfluidic (DMF) devices are an attractive platform to apply the promising benefits of enzymatic oligonucleotide synthesis to the manufacturing of synthetic DNA. This thesis work aims to demonstrate automated DNA assembly using oligonucleotides on a DMF device through the demonstration and validation of an automated DNA assembly protocol. The prototyping process performed through this work revealed various important design considerations for the reliability of fluid handling performance and the mitigation of failure modes. To prevent dielectric breakdown or electrolysis, a relatively thick SU-8 3005 dielectric is used to remove the sensitivity of the device to variances in dielectric thickness and quality. To enable droplet creation, the gap distance between the DMF chip and top-plate is created and minimized using a thick SU-8 2100 layer. Reliable droplet creation is achieved through the use of electrode geometry that targets predictable fluid delivery and cutting. Reliable droplet transport is achieved through the use of a electrode interdigitation geometry that targets lower total electrode surface area and higher interdigitation contact area. The testing of DNA laden fluids revealed that biofouling can be a large concern for the demonstration of DNA assembly on a DMF device if droplets are moved through an air medium. To mitigate its effects, the final DMF device design featured the use of a permanently bonded top-plate with bored inlet/outlet ports as well as a silicone oil medium. The final DMF device design was used to demonstrate automated DNA assembly. This demonstration involved the creation, transport, and mixing of DNA brick samples. These samples are subsequently incubated on a chemical bench or on the DMF chip to create recombinant DNA containing genetic information. DNA gel imaging of DNA assembly products from on-chip protocols compared to protocols performed on a chemical benchtop revealed comparable results. Through the course of this work, the applicability of automated DNA assembly on a DMF device was validated to provide preliminary results in the ultimate goal of DNA synthesis using enzymatic oligonucleotide synthesis

System Integration - A Major Step toward Lab on a Chip

Microfluidics holds great promise to revolutionize various areas of biological engineering, such as single cell analysis, environmental monitoring, regenerative medicine, and point-of-care diagnostics. Despite the fact that intensive efforts have been devoted into the field in the past decades, microfluidics has not yet been adopted widely. It is increasingly realized that an effective system integration strategy that is low cost and broadly applicable to various biological engineering situations is required to fully realize the potential of microfluidics. In this article, we review several promising system integration approaches for microfluidics and discuss their advantages, limitations, and applications. Future advancements of these microfluidic strategies will lead toward translational lab-on-a-chip systems for a wide spectrum of biological engineering applications

Self-propelling surfactant droplets in chemically-confined microfluidics – cargo transport, drop-splitting and trajectory control

We demonstrate the applicability of self-propulsion as a passive driving mechanism for droplets in chemically-confined microfluidics. The droplets can be used to transport considerably sized solid cargo particles. We implemented thermal actuation as a steering mechanism for the droplets at fluidic junctions

New Application for Indium Gallium Zinc Oxide thin film transistors: A fully integrated Active Matrix Electrowetting Microfluidic Platform

The characterization and fabrication of active matrix TFTs [Thin Film Transistors] have been studied for applying an addressable microfluidic electrowetting channel device. The a-IGZO [Amorphous Indium Gallium Zinc Oxide] is used for electronic switching device to control the microfluidic device because of its high mobility, transparency, and easy to fabrication. The purpose of this dissertation is to optimize each IGZO TFT process including the optimization of a-IGZO properties to achieve robust device for application. To drive the IGZO TFTs, the channel resistance of IGZO layer and contact resistance between IGZO layer and source/drain (S/D) electrode are discussed in this dissertation. In addition, the generalization of IGZO sputter condition is investigated by calculation of IGZO and O2 [Oxygen] incorporation rate at different oxygen partial pressure and different sputter targets. To develop the robust IGZO TFTs, the different passivation layers deposited by RF [Radio Frequency] magnetron sputter are investigated by comparing the electrical characteristics of TFTs. The effects PECVD [Plasma Enhanced Chemical Vapor Deposition] of SiO2 [Silicon Dioxide] passivation layers on IGZO TFTs is studied the role of hydrogen and oxygen with analyzed and compared the concentration by the SIMS [Secondary Ion Mass Spectroscopy]. In addition, the preliminary electrowetting tests are performed for electrowetting phenomena, the liquid droplet actuation, the comparison between conventional electrowetting and Laplace barrier electrowetting, and the different size electrode effect for high functional properties. The active matrix addressing method are introduced and investigated for driving the electrowetting microfluidic channel device by Pspice simulation. Finally, the high resolution electrowetting microfluidic device (16ⅹ16 matrix) is demonstrated by driving liquid droplet and channel moving using active matrix addressing method and fully integrated IGZO TFTs

Digital Microfluidic (DMF) devices based on electrowetting on dielectric (EWOD) for biological applications

Microfluidic devices have been used in various applications including automated analysis systems, biological applications like DNA sequencing, antigen-antibody reactions, protein studies, chemical applications, single cell studies, etc. Microfluidic devices are primarily categorised into two types. First are continuous microfluidic devices. These devices consist of predefined microchannels, micro-valves, and syringe pumps. Fluid is continuously flowing in these channels. The second type is digital microfluidic platforms. In this type, MXN array of electrodes is patterned on non-conducting substrate. Fluid is discretized to form tiny droplets. These droplets are transported, mixed and split using external electric field. Digital microfluidic devices are configurable as there are no permanently etched channels. Also, they have high throughput. Multiple reactions can be performed on the same platform at the same time. The time taken to complete one reaction is less compared to the continuous devices. Thus they help in faster analysis. These devices are controlled by electrical field and thus unlike continuous devices, digital microfluidic devices are free from mechanically moving parts. Digital microfluidic devices may suffer from charge accumulation due to electrostatic forces. Also, voltage levels applied play an important role. The applied voltage has to be enough to move droplets but should not cause electrolysis of the liquid used. Also voltage switching time between electrodes and frequency applied are important. These parameters can change the mixing quality. In this work, 2D simulations of droplet manipulation due to voltage application, transport and mixing are carried out. Also digital microfluidic device is designed and fabricated to carry out biological mixing experiments

Microvortices In Droplets: Generation & Applications

The emerging field of droplet microfluidics deals with the manipulation of nL-fL droplets encapsulated within an immiscible carrier phase. The droplets are used as reaction containers for biochemical assays, enabling drastic reduction in assay volumes needed for modern life sciences research. To achieve this, basic laboratory processes such as mixing, detection, and metering must be emulated in the droplet format. Three important unit operations relevant to high throughput screening include 1) the concentration of particles and species within droplets, which is necessary for heterogeneous assays; 2) sensing the biochemical contents of a droplet; and 3) the sorting of droplets based on physical or chemical properties, which is important for single cell and proteomic assays. Currently, particle concentration in droplets requires active components, such as on-chip electrodes or magnets, along with charged or magnetic particles. Similarly, sensing and sorting droplets by chemical composition is based on flow cytometry, which also requires on-chip electrodes, feedback control, and chemical labeling. It is desirable to avoid active field techniques due to complexity, size, and cost constraints, and replace them with more simple and passive techniques. In this thesis, we utilize microvortices, the rotational motion of fluid, to enhance the capabilities of droplet microfluidics in the above three areas. The microvortices are generated using two methods: (i) hydrodynamic recirculation drag and (ii) tensiophoresis. In the first method, species concentration is accomplished by exploiting the shear-induced vortices that occur naturally inside a droplet/plug as it moves through a microchannel. Prior studies utilized these flows for enhancing mixing or interphase mass transfer. This work exploits microvortices together with two other independent phenomena--sedimentation of particles and interfacial adsorption of proteins--to concentrate both types of species at the rear of the droplet, where they can be extracted from the drop. In the latter case, the protein localization at the rear of drop reduces the interfacial tension locally resulting in an asymmetry in the drop shape. Under laminar flow, the shape deformation is deterministic and can serve as a sensitive, label-free indicator of protein concentration in proteomic screening. In the second method, label-free sorting of droplets is accomplished by a novel droplet actuation technique termed Tensiophoresis. A microchemical gradient across the droplet is transduced into a microvortex flow which propels the droplets up the chemical gradient. Using laminar flow to precisely control the gradient, droplets can be sorted by size with 3.3% resolution over a wide turning range. Droplets can be also sorted based on chemical composition because tensiophoresis is inhibited by surface active agents adsorbed on the droplet surface. Studies conducted using Bovine Serum Albumin (BSA) show that the droplet migration velocity scales inversely with protein concentration in the droplet, and migration velocity can be correlated to protein concentration with a 1 femtomole limit of detection. As modern life sciences research becomes increasingly reliant on high throughput workflows, microdroplet technology can meet the growing demand to perform screening at ultra-high throughputs with reduced sample volume. This thesis contributes three important unit operations which expand the capabilities of droplet-based workflows in proteomics, cell biology, and other areas of biomedical research

MICROPARTICLE SAMPLING AND SEAPARATIONENABLED BY DROPLET MICROFLUIDICS

This work reports design, device fabrication, modeling and experimental results on newsampling and separation principles in which liquid is transported in a droplet form on a plannerhydrophobic surface with no moving parts. The presented particle sampler and separatorconstitute core units for the handheld lab-on-a-chip-based airborne particle monitoring system.For the airborne particle sampling, a novel method is developed by which the particles onthe solid surface are swept and sampled by electrowetting-actuated moving droplets. Theoreticalanalysis and experimental works along with microfabricated testing devices are carried out toinvestigate the underlying physics and to optimize the sampling conditions. The samplingconcepts are examined and proved on a solid surface and perforated filter membrane showinghigh sampling efficiencies.For the particle separation, a new separation scheme is developed in which the mixedparticles are separated within a mother droplet by traveling-wave dielectrophoresis (tw-DEP).Using the subsequent operation of droplet splitting by way of electrowetting, the separatedparticles can be isolated into each split droplet according to the DEP properties of the particles.This in-droplet separation is examined with many combinations of particles in microfabricateddevices. By investigating the particle behavior as function of the frequency of the traveling waveDEP signal, the separation efficiencies are optimized.The above microfluidic units constitute key components for upstream particle sampling anddownstream sample processing in the lab on a chip system, providing the following advantages:extremely small amount use of samples/reagents (2) no external pressure source required forfluidic operations, (3) simple design and fabrication since no mechanical moving structure

BioScript: programming safe chemistry on laboratories-on-a-chip

This paper introduces BioScript, a domain-specific language (DSL) for programmable biochemistry which executes on emerging microfluidic platforms. The goal of this research is to provide a simple, intuitive, and type-safe DSL that is accessible to life science practitioners. The novel feature of the language is its syntax, which aims to optimize human readability; the technical contributions of the paper include the BioScript type system and relevant portions of its compiler. The type system ensures that certain types of errors, specific to biochemistry, do not occur, including the interaction of chemicals that may be unsafe. The compiler includes novel optimizations that place biochemical operations to execute concurrently on a spatial 2D array platform on the granularity of a control flow graph, as opposed to individual basic blocks. Results are obtained using both a cycle-accurate microfluidic simulator and a software interface to a real-world platform