Digital microfluidic devices: the role of the dielectric layer

Digital microfluidics (DMF) is a field which has emerged in the last decade as a re-liable and versatile tool for sensing applications based on liquid reactions. DMF allows the discrete displacement of droplets, over an array of electrodes, by the application of voltage, and also the dispensing from a reservoir, mixing, merging and splitting fluidic operations. The main drawback of these devices is due to the need of high driving volt-ages for droplet operations. In this work, alternative dielectric layers combinations were studied aiming the reduction of these driving voltages. DMF chips were designed, pro-duced and optimized according to the theory of electrowetting-on-dielectric, adopting different combinations of parylene-C and tantalum pentoxide (Ta2O5) as dielectric ma-terials, and Teflon as hydrophobic layer. With both devices’ configurations, i.e., Parylene as single dielectric, and multilayer chips combining Parylene and Ta2O5, it was possible to perform all the fluidic opera-tions in the microliter down to hundreds of nanoliters range. Multilayer chips presented significant reduction on driving voltages for droplet op-erations in silicone oil filler medium: from 70 V (parylene only) down to 30 V (parylene/Ta2O5) for dispensing; and from 50 V (parylene only) down to 15 V (parylene/Ta2O5) for movement. Peroxidase colorimetric reactions were successfully performed as proof-of-concept, using multilayer configuration devices

Surface Properties of Nanopore-Structured Metals and Oxides

The importance of understanding the properties of textured surfaces is growing with their potential wide engineering applications. In this thesis research, nanopore structures of metals and oxides were examined to determine the interactions between environmental object and the textured surfaces. The major applications of nanopore structures are micro/nanoelectromechanical systems (MEMS/NEMS), energy devices, sensors, and environmental devices. In order to achieve better performance in each, it needs to consider three critical surface properties such as surface forces, electrochemical performances, and wettability. In this research, the surface properties of nanopore structures have been explored with understanding the essence of contact. This research uses experimental approach combined with basic analysis in physical principles. Experiments include fabrication of nanopore structures, investigation of surface force, electrochemical evaluation, and wetting/electrowetting studies of nanopore structures. Metallic nanopore structures (MNSs) of nickel were characterized by using an atomic force microscope (AFM) and a triboscope. The mechanisms of bacteria desorption were examined by alumina nanopore structures (ANSs) with various pore sizes. The kinetics of ion-transfer on MNSs was studied using Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltametry (CV). The (electro-) wetting behavior of MNSs were examined using a droplet shape measurement system. A physics based analysis was conducted in order to understand the principles of the nanopore effects on environments suitable for various applications. Results lead to the successful identification of critical geometrical factors. A contact model has been established to understand properties of textured surfaces. Specific design factors, which are related to the geometry of the textured surfaces has been identified. This research revealed fundamental mechanisms of contact and establish a relationship between morphology/geometry and surface properties. The findings in this thesis research afford new approach to optimize applications of textured surface. The proposed contact models are beneficial to the surface design and application of sustainable micro/nanodevices. This thesis includes eight chapters. The first chapter introduces the background and fundamental knowledge related to current research in order to understand the basics. Followed by the chapter two of motivation and objectives, chapter three discusses materials and experimental details, chapter four and five cover the surface forces, chapter six studies the electrochemical performances, chapter seven investigates the (electro-)wettability, and the conclusions and future recommendations are presented in chapter eight

Surface Properties of Nanopore-Structured Metals and Oxides

The importance of understanding the properties of textured surfaces is growing with their potential wide engineering applications. In this thesis research, nanopore structures of metals and oxides were examined to determine the interactions between environmental object and the textured surfaces. The major applications of nanopore structures are micro/nanoelectromechanical systems (MEMS/NEMS), energy devices, sensors, and environmental devices. In order to achieve better performance in each, it needs to consider three critical surface properties such as surface forces, electrochemical performances, and wettability. In this research, the surface properties of nanopore structures have been explored with understanding the essence of contact. This research uses experimental approach combined with basic analysis in physical principles. Experiments include fabrication of nanopore structures, investigation of surface force, electrochemical evaluation, and wetting/electrowetting studies of nanopore structures. Metallic nanopore structures (MNSs) of nickel were characterized by using an atomic force microscope (AFM) and a triboscope. The mechanisms of bacteria desorption were examined by alumina nanopore structures (ANSs) with various pore sizes. The kinetics of ion-transfer on MNSs was studied using Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltametry (CV). The (electro-) wetting behavior of MNSs were examined using a droplet shape measurement system. A physics based analysis was conducted in order to understand the principles of the nanopore effects on environments suitable for various applications. Results lead to the successful identification of critical geometrical factors. A contact model has been established to understand properties of textured surfaces. Specific design factors, which are related to the geometry of the textured surfaces has been identified. This research revealed fundamental mechanisms of contact and establish a relationship between morphology/geometry and surface properties. The findings in this thesis research afford new approach to optimize applications of textured surface. The proposed contact models are beneficial to the surface design and application of sustainable micro/nanodevices. This thesis includes eight chapters. The first chapter introduces the background and fundamental knowledge related to current research in order to understand the basics. Followed by the chapter two of motivation and objectives, chapter three discusses materials and experimental details, chapter four and five cover the surface forces, chapter six studies the electrochemical performances, chapter seven investigates the (electro-)wettability, and the conclusions and future recommendations are presented in chapter eight

Characterization of advanced materials for low-frequency Vibrational Energy Harvesting (VEH)

openNowadays sensors are among the most exploited systems in everyday life, with several applications stimulating an increasing amount of research. They generally require external power, thus adding issues such as maintenance and size constraints. The most promising energy harvesting (EH) technology for miniaturization is Reverse Electro wetting on Dielectric (REWoD). It can provide high power density by exploiting the mechanical modulation of the capacity at the liquid/dielectric interface attaining, without any external bias, power densities of µW/cm2. With respect to other EH techniques, REWoD harvests energy from low frequency vibrations (< 10Hz, human motion). I exploited low-cost materials as proof of concept of the feasibility of vibrational EH, suitable for wearable devices, using highly hydrophobic Al and PVDF coated electrodes in combination with polyacrylamide (PAAm) hydrogels loaded with LiCl solutions. The morphology at the sub-micrometer scale and the composition of the outer layers of Al have been studied as a function of the chemical etching time and have been correlated with the surface wettability. The etched Al surfaces exhibit binary structures with nanoscale block-like convexes and hollows, providing more space for air trapping. The analysis shows not only that the change in wetting behaviour correlates with the amount of Al hydroxide at the surface, but also confirms the essential role of the adsorption of airborne carbon compounds. The hydrophobic behaviour depends therefore on the combined effects of surface morphology and surface chemical composition. To compensate for the degradation of the hydrogels with time due to the microstructure of the external oxide layer, an alternative bare Al electrode covered with PVDF has been tested: PAAm hydrogels show now no degradation with time while being able to provide, at frequencies lower than 10 Hz, a peak power/unity of 0.6 Watt, higher than 0.25 Watt, obtained by using the Al oxide electrode.openXXXIII CICLO - SCIENZE E TECNOLOGIE DELLA CHIMICA E DEI MATERIALI - Scienza e tecnologia dei materialiPaolini, Giuli

The Application Of Graphene Films In Biosensing And Electrowetting

In recent years, graphene has been found to possess extraordinary electronic, optical, mechanical and electrochemical properties. Graphene is optically transparent and mechanically flexible, and has high electron mobility and conductivity. In this thesis, we propose to investigate graphene\u27s properties in the detection of biomolecules as well as the manipulation of biological samples. Graphene without defects has high charge carrier mobility and surface areas, which is ideal for biosensors. However, literature shows a lot of variations in the measurements using graphene biosensors. In addition, the surface functionalization of graphene in order to enhance the specificity has not been fully investigated yet. We propose to combine e-beam lithography (EBL) and dry etching to generate edge defects for biosensor application. These edge defects not only enhance sensitivity but also control the binding sites for surface functionalization. We also demonstrate, for the first time, a microfluidic device based on electrowetting-on-dielectric (EWOD) using a graphene electrode. Hydrophobic surfaces of graphene facilitate self-assembly of the hydrophobic dielectric layer (Teflon). Using graphene electrode, we are able to achieve robust and reversible changes in contact angle without electrolysis. Graphene enables the manipulation of droplets on flexible and transparent substrates using low-cost PET (polyethylene terephthalate). With its high optical transparency, mechanical flexibility and excellent electrical properties, graphene may be suitable in the manipulation of biological samples and in the detection of biomolecules. The research may be applicable in the development of the next generation point-of-care device

Parylene C as a Multipurpose Material for Electronics and Microfluidics

Funding Information: This work was financed by national funds from FCT—Fundação para a Ciência e a Tecnologia, I.P., in the scope of the projects LA/P/0037/2020, UIDP/50025/2020 and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication—i3N. Furthermore, the work received funding from FCT in the scope of projects UIDP/04378/2020 and UIDB/04378/2020 of the Research Unit on Applied Molecular Biosciences—UCIBIO and the project LA/P/0140/2020 of the Associate Laboratory Institute for Health and Bioeconomy—i4HB. This work also received funding from the European Community’s H2020 program under grant agreements 716510 (ERC-2016-StG TREND), 787410 (ERC-2019-AdG DIGISMART) and 952169 (SYNERGY, H2020-WIDESPREAD-2020-5, CSA), 101008701 (EMERGE, H2020-INFRAIA-2018-2020). B. J. Coelho acknowledges FCT for the attribution of grant SFRH/BD/132904/2017 and grant COVID/BD/152453/2022. Publisher Copyright: © 2023 by the authors.Poly(p-xylylene) derivatives, widely known as Parylenes, have been considerably adopted by the scientific community for several applications, ranging from simple passive coatings to active device components. Here, we explore the thermal, structural, and electrical properties of Parylene C, and further present a variety of electronic devices featuring this polymer: transistors, capacitors, and digital microfluidic (DMF) devices. We evaluate transistors produced with Parylene C as a dielectric, substrate, and encapsulation layer, either semitransparent or fully transparent. Such transistors exhibit steep transfer curves and subthreshold slopes of 0.26 V/dec, negligible gate leak currents, and fair mobilities. Furthermore, we characterize MIM (metal–insulator–metal) structures with Parylene C as a dielectric and demonstrate the functionality of the polymer deposited in single and double layers under temperature and AC signal stimuli, mimicking the DMF stimuli. Applying temperature generally leads to a decrease in the capacitance of the dielectric layer, whereas applying an AC signal leads to an increase in said capacitance for double-layered Parylene C only. By applying the two stimuli, the capacitance seems to suffer from a balanced influence of both the separated stimuli. Lastly, we demonstrate that DMF devices with double-layered Parylene C allow for faster droplet motion and enable long nucleic acid amplification reactions.publishersversionpublishe

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 Microfluidics for Isothermal Nucleic Acid Amplification: Exploring Sensing Methodologies

Digital Microfluidics (DMF) has recently emerged as a promising candidate for nucleic acid amplification for molecular diagnostics, by virtue of its precise control over unit droplets without the need of any propulsion devices, ease of integration with chemical/biological reac-tions and multiplex assay capabilities. Nevertheless, current scientific research is still far from accomplishing the full potential of the technique, so new, innovative nanotechnology/biotech-nology hybrid approaches are necessary. As such, the purpose of this work is to contribute for the paradigm shift of nucleic acid amplification from central laboratories to point-of-care (POC) by designing and fabricating DMF devices compatible with isothermal nucleic acid amplifica-tion (loop-mediated isothermal amplification - LAMP). For biological validation of the devices, detection of cancer biomarker c-Myc is performed, and further real-time amplification moni-toring is attempted through several methodologies, namely fluorescence, impedance and elec-trochemical measurements. The DMF devices produced herein enable optimal temperature control, crucial for LAMP reactions, and further allow for a novel methodology of reagent mix-ing, based on dual actuation with back-and-forth motion and actuation frequency tuning. Such innovations lead to successful amplification of 0.5 ng/μL or 90 pg of c-Myc in one hour, in line with the range reported in the literature, and further monitoring of the LAMP reaction profile by microscopy-based fluorescence measurements. Impedimetric and electrochemical method-ologies did not meet the tight criteria required for biomarker detection, yet the developments achieved herein open the path for other applications. Lastly, the dielectric layer (key element of a DMF device) was optimized to assure long reactions (up to two hours) without device degradation.A microfluídica digital (MFD) surgiu como uma tecnologia promissora para amplificação de ácidos nucleicos em diagnóstico molecular, permitindo controlo sobre gotas unitárias sem necessidade de dispositivos de propulsão, facilidade de integração com reações químicas/bi-ológicas e capacidade de realização de ensaios simultâneos. Contudo, a investigação científica atual ainda está longe de atingir o máximo potencial da técnica, pelo que são necessárias abordagens novas, inovadoras e híbridas de nanotecnologia e biotecnologia. Como tal, o pro-pósito deste trabalho é contribuir para a mudança de paradigma da amplificação de ácidos nucleicos de laboratórios centralizados para ponto-de-atendimento (PDA) através do desenho e fabricação de dispositivos de MFD compatíveis com amplificação isotérmica de ácidos nu-cleicos (loop-mediated istothermal amplification - LAMP). Para validação biológica dos dispo-sitivos, será detetado o biomarcador de cancro c-Myc, e testada a monitorização da amplifica-ção em tempo real através de várias metodologias, nomeadamente medidas de fluorescência, impedância ou medidas eletroquímicas. Os dispositivos MFD produzidos permitem um con-trolo ótimo da temperatura, crucial para reações LAMP, e introduzem uma metodologia para mistura de reagentes, com movimentos em vaivém e ajuste da frequência de atuação. Tais inovações conduziram à amplificação de 0.5 ng/μL ou 90 pg de c-Myc em uma hora, em linha com o intervalo relatado na literatura, permitindo ainda monitorização do perfil da reação LAMP através de medidas de fluorescência mediadas por microscopia. As metodologias impe-dimétricas e eletroquímicas não cumpriram os exigentes critérios requeridos para deteção de biomarcadores, no entanto, os desenvolvimentos alcançados abrem caminho para outras apli-cações. Por último, a camada dielétrica (elemento-chave de um dispositivo MFD) foi otimizada para assegurar reações mais longas (até duas horas) sem degradação do dispositivo