Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Peclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.

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Microfluidics: Fluid physics at the nanoliter scale

Microfluidic devices for manipulating fluids are widespread and finding uses in many scientific and industrial contexts. Their design often requires unusual geometries and the interplay of multiple physical effects such as pressure gradients, electrokinetics, and capillarity. These circumstances lead to interesting variants of well-studied fluid dynamical problems and some new fluid responses. We provide an overview of flows in microdevices with focus on electrokinetics, mixing and dispersion, and multiphase flows. We highlight topics important for the description of the fluid dynamics: driving forces, geometry, and the chemical characteristics of surfaces.

Engineering flows in small devices

基礎講座 電気泳動(Electrophoresis)

It is important to realize that guidelines cannot always account for individual variation among patients. They are not intended to supplant physician judgment with respect to particular patients or special clinical situations. IDSA considers adherence to these guidelines to be voluntary, with the ultimate determination regarding their application to be made by the physician in the light of each patient's individual circumstances.

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Clinical Practice Guideline for the Management of Candidiasis: 2016 Update by the Infectious Diseases Society of America

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.

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Electrowetting: from basics to applications

We present a liquid droplet mixer to enable mixing of the samples and reagents for chemical and biological analysis in micro total analysis systems (/spl mu/TAS). The droplets in the mixer are actuated based on electrowetting phenomenon. The actuator comprises of two parallel glass plates between which the droplet is actuated on a planar array of electrodes. Mixing of liquid channels in microfluidic systems has been demonstrated for continuous flow systems where the mixing is diffusion-limited due to the laminar flow of liquids, requiring very long, thin channels. In the present paper, mixing is performed on discrete droplets of liquid. When two droplets are brought together, depending on the velocity of the moving droplets, surface tension, viscosity, electrode activation, and volume among other factors, turbulence is created which aids in mixing. The mixing is not limited by diffusion and enhanced by transport. The mixing experiments are performed between fluorescein and plain water droplets whose individual volume is 1.75 /spl mu/l. Mixing is visualized with a 2-CCD camera setup to observe both the top and side views, with appropriate filters to capture fluorescence. We observed that it takes about 60 seconds for two droplets of 1.75 /spl mu/l each to mix when their surface tensions are different and it takes about 90 seconds when the two droplets have similar surface tensions. The present mixer stands apart from any current conventional micromixers in that the mixing times occupies much lesser area, mixing does not need any specific architecture on the chip and can be performed on any transport electrodes dynamically assigned to mixing.

Microfluidic electrowetting-based droplet mixing

The invention provides a droplet actuator drive. In certain embodiments, the droplet actuator drive may include a detection apparatus for sensing a property of a droplet on a droplet actuator; circuitry for controlling the detection apparatus electronically coupled to the detection apparatus; a droplet actuator cartridge connector; circuitry for controlling a droplet actuator coupled to the droplet actuator connector; and/or a means for coupling the droplet actuator circuitry to a processor. Systems, kits and methods of conducting assays are also provided.

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Modular droplet actuator drive

On-board reagent storage, handling, and dispensing apparatuses and methods for droplet actuator systems are provided. In one embodiment, a fluidic analyzer is provided and includes a droplet actuator including a substrate including a plurality of electrodes configured to actuate a droplet and a reagent storage component in selective fluid communication with the droplet actuator and including a reagent configured to combine with a solvent at a time of use. In another embodiment, a method of conducting fluidic analysis is provided and includes storing a reagent within a reagent storage component in fluid communication with a droplet actuator including a plurality of electrodes configured to actuate a droplet and combining the reagent with a solvent at a time for use within the droplet actuator.

Reagent storage and reconstitution for a droplet actuator

https://dukespace.lib.duke.edu/dspace/bitstream/handle/10161/11070/DMID-67-22-10.pdf;sequence=1

Microfluidic platform versus conventional real-time polymerase chain reaction for the detection of Mycoplasma pneumoniae in respiratory specimens.

A droplet actuator with arrays of electrodes electrically coupled to a number of controllable voltage sources that is less than the number of electrodes. A method of defining partitions for pin layouts in a droplet actuator for a specific assay, the method including: defining droplet traces for the assay; and defining a guard ring along the traces. Other methods, systems, droplet actuators, and algorithms are also provided.

Michael G. Pollack

Papers

Microfluidic electrowetting-based droplet mixing

Modular droplet actuator drive

Reagent storage and reconstitution for a droplet actuator

Microfluidic platform versus conventional real-time polymerase chain reaction for the detection of Mycoplasma pneumoniae in respiratory specimens.

Droplet actuators, systems and methods