Bio: Tom Korsmeyer is an academic researcher. The author has contributed to research in topics: Dielectrophoresis & Electrowetting. The author has an hindex of 1, co-authored 1 publications receiving 292 citations.
TL;DR: This study shows that both electrowetting on dielectric and dielectrophoresis are effective for droplet generation and manipulation, and demonstrates: (1) the presence of a wetting contribution to dielectophoresis; and (2) contact angle reduction is merely an observable consequence of, not a condition for, the occurrence of electrowsetting onDielectric.
Abstract: Electrically controlled droplet-based labs-on-a-chip operate under the principles of electro-capillarity and dielectrophoresis. The microfluidic mechanics of manipulating electrified droplets are complex and not entirely understood. In this article, we analyse these operating principles, especially electrowetting on dielectric (a form of electro-capillarity) and dielectrophoresis, under a unified framework of droplet electrohydrodynamics. We differentiate them by their electric origins and their energy transduction mechanisms. Our study shows that both electrowetting on dielectric and dielectrophoresis are effective for droplet generation and manipulation. In addition, our study demonstrates: (1) the presence of a wetting contribution to dielectrophoresis; and (2) contact angle reduction is merely an observable consequence of, not a condition for, the occurrence of electrowetting on dielectric. Simulations are used extensively in this article to illustrate device operation, to expose underlying physics, and to validate our conclusions. Simulations of electrically driven droplet generation, droplet translocation, droplet fusion, and droplet fission are presented.
TL;DR: In this paper, the authors compare the various approaches used to derive the basic electrowetting equation, which has been shown to be very reliable as long as the applied voltage is not too high.
Abstract: Electrowetting has become one of the most widely used tools for manipulating tiny amounts of liquids on surfaces. Applications range from 'lab-on-a-chip' devices to adjustable lenses and new kinds of electronic displays. In the present article, we review the recent progress in this rapidly growing field including both fundamental and applied aspects. We compare the various approaches used to derive the basic electrowetting equation, which has been shown to be very reliable as long as the applied voltage is not too high. We discuss in detail the origin of the electrostatic forces that induce both contact angle reduction and the motion of entire droplets. We examine the limitations of the electrowetting equation and present a variety of recent extensions to the theory that account for distortions of the liquid surface due to local electric fields, for the finite penetration depth of electric fields into the liquid, as well as for finite conductivity effects in the presence of AC voltage. The most prominent failure of the electrowetting equation, namely the saturation of the contact angle at high voltage, is discussed in a separate section. Recent work in this direction indicates that a variety of distinct physical effects?rather than a unique one?are responsible for the saturation phenomenon, depending on experimental details. In the presence of suitable electrode patterns or topographic structures on the substrate surface, variations of the contact angle can give rise not only to continuous changes of the droplet shape, but also to discontinuous morphological transitions between distinct liquid morphologies. The dynamics of electrowetting are discussed briefly. Finally, we give an overview of recent work aimed at commercial applications, in particular in the fields of adjustable lenses, display technology, fibre optics, and biotechnology-related microfluidic devices.
TL;DR: To understand the opportunities and limitations of EWD microfluidics, this paper looks at the development of lab-on-chip applications in a hierarchical approach.
Abstract: The suitability of electrowetting-on-dielectric (EWD) microfluidics for true lab-on-a-chip applications is discussed. The wide diversity in biomedical applications can be parsed into manageable components and assembled into architecture that requires the advantages of being programmable, reconfigurable, and reusable. This capability opens the possibility of handling all of the protocols that a given laboratory application or a class of applications would require. And, it provides a path toward realizing the true lab-on-a-chip. However, this capability can only be realized with a complete set of elemental fluidic components that support all of the required fluidic operations. Architectural choices are described along with the realization of various biomedical fluidic functions implemented in on-chip electrowetting operations. The current status of this EWD toolkit is discussed. However, the question remains: which applications can be performed on a digital microfluidic platform? And, are there other advantages offered by electrowetting technology, such as the programming of different fluidic functions on a common platform (reconfigurability)? To understand the opportunities and limitations of EWD microfluidics, this paper looks at the development of lab-on-chip applications in a hierarchical approach. Diverse applications in biotechnology, for example, will serve as the basis for the requirements for electrowetting devices. These applications drive a set of biomedical fluidic functions required to perform an application, such as cell lysing, molecular separation, or analysis. In turn, each fluidic function encompasses a set of elemental operations, such as transport, mixing, or dispensing. These elemental operations are performed on an elemental set of components, such as electrode arrays, separation columns, or reservoirs. Examples of the incorporation of these principles in complex biomedical applications are described.
TL;DR: It is demonstrated that surface acoustic waves (SAWs), nanometer amplitude Rayleigh waves driven at megahertz order frequencies propagating on the surface of a piezoelectric substrate, offer a powerful method for driving a host of extremely fast microfluidic actuation and microbioparticle manipulation schemes.
Abstract: We demonstrate that surface acoustic waves (SAWs), nanometer amplitude Rayleigh waves driven at megahertz order frequencies propagating on the surface of a piezoelectric substrate, offer a powerful method for driving a host of extremely fast microfluidic actuation and microbioparticle manipulation schemes. We show that sessile drops can be translated rapidly on planar substrates or fluid can be pumped through microchannels at 1-10 cms velocities, which are typically one to two orders quicker than that afforded by current microfluidic technologies. Through symmetry-breaking, azimuthal recirculation can be induced within the drop to drive strong inertial microcentrifugation for micromixing and particle concentration or separation. Similar micromixing strategies can be induced in the same microchannel in which fluid is pumped with the SAW by merely changing the SAW frequency to rapidly switch the uniform through-flow into a chaotic oscillatory flow by exploiting superpositioning of the irradiated sound waves from the sidewalls of the microchannel. If the flow is sufficiently quiescent, the nodes of the transverse standing wave that arises across the microchannel also allow for particle aggregation, and hence, sorting on nodal lines. In addition, the SAW also facilitates other microfluidic capabilities. For example, capillary waves excited at the free surface of a sessile drop by the SAW underneath it can be exploited for micronanoparticle collection and sorting at nodal points or lines at low powers. At higher powers, the large accelerations off the substrate surface as the SAW propagates across drives rapid destabilization of the drop free surface giving rise to inertial liquid jets that persist over 1-2 cm in length or atomization of the entire drop to produce 1-10 mum monodispersed aerosol droplets, which can be exploited for ink-jet printing, mass spectrometry interfacing, or pulmonary drug delivery. The atomization of polymerprotein solutions can also be used for the rapid synthesis of 150-200 nm polymerprotein particles or biodegradable polymeric shells in which proteins, peptides, and other therapeutic molecules are encapsulated within for controlled release drug delivery. The atomization of thin films behind a translating drop containing polymer solutions also gives rise to long-range spatial ordering of regular polymer spots whose size and spacing are dependent on the SAW frequency, thus offering a simple and powerful method for polymer patterning without requiring surface treatment or physicalchemical templating.
TL;DR: In this paper, a review of the electrowetting-on-dielectric (EWOD) actuation mechanism is presented, which summarizes the observations, insights, and modeling techniques that have led to the current picture showing how forces act on liquid droplets and how droplets respond in EWOD microfluidic devices.
Abstract: This paper reviews publications that have fortified our understanding of the electrowetting-on-dielectric (EWOD) actuation mechanism. Over the last decade, growing interest in EWOD has led to a wide range of scientific and technological investigations motivated by its applicability in microfluidics, especially for droplet-based optical and lab-on-a-chip systems. At this point in time, we believe that it is helpful to summarize the observations, insights, and modeling techniques that have led to the current picture showing how forces act on liquid droplets and how droplets respond in EWOD microfluidic devices. We discuss the basic physics of EWOD and explain the mechanical response of a droplet using free-body diagrams. It is our hope that this review will inspire new research approaches and help design useful devices.
TL;DR: How dielectrophoresis and AC electrokinetics can be used in droplet-based microfluidic chips, biosensors, and devices for collection of particles from diluted suspensions is discussed.
Abstract: We overview the ways in which electric fields can be used for on-chip manipulation and assembly of colloidal particles. Particles suspended in water readily respond to alternating (AC) or direct current (DC) electric fields. Charged particles in DC fields are moved towards oppositely charged electrodes by electrophoresis. Dielectrophoresis, particle mobility in AC fields, allows precise manipulation of particles through a range of parameters including field strength and frequency and electrode geometry. Simultaneously, DC or AC electrokinetics may drive liquid flows inside the experimental cells, which also leads to transport and redistribution of the suspended particles. Examples of dielectrophoretic manipulation and assembly of nanoparticles and microparticles by planar on-chip electrodes are presented. The structures assembled include conductive microwires from metallic nanoparticles and switchable two-dimensional crystals from polymer microspheres. We also discuss how dielectrophoresis and AC electrokinetics can be used in droplet-based microfluidic chips, biosensors, and devices for collection of particles from diluted suspensions.