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.

/pdf/clinical-practice-guideline-for-the-management-of-451dfbrsff.pdf

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.

/pdf/electrowetting-from-basics-to-applications-14e6zoxse5.pdf

Electrowetting: from basics to applications

The present invention relates to surface assisted fluid loading and droplet dispensing on a droplet micro actuator. A droplet actuator is provided and includes one or more electrodes configured for conducting one or more droplet operations on a droplet operations surface of the substrate. The droplet actuator further includes a wettable surface defining a path from a fluid reservoir into a locus which is sufficiently near to one or more of the electrodes that activation of the one or more electrodes results in a droplet operation. Methods and systems are also provided.

Surface assisted fluid loading and droplet dispensing

VVe present the use of optical coherence tomography (OCT), an interferometric 3-D imaging technique, to visualize microdroplets in an electrowetting-based microfluidic device. Vertical cross-sectional images of stationary and moving microdroplets are obtained using this technique, to provide information on static and dynamic contact angle changes and flow profiles inside the microdroplet during transport. The initial results are encouraging and OCT appears to be a promising method to study fundamental, yet poorly understood electrowetting phenomena such as contact angle saturation and contact angle hysteresis. OCT can also be used in visualizing 3-D flow profiles in droplet-based microfluidics.

https://www.rsc.org/binaries/loc/2003/Volume2/108-359.pdf

3-d imaging of moving droplets for microfluidics using optical coherence tomography

The invention provides a droplet actuator device, as well as systems, methods and devices making use of the droplet actuator device. The droplet actuator device may include a substrate having electrodes arranged for conducting one or more droplet operations. The droplet actuator device may include a substrate having a reactor path with a wash region associated with a magnet for immobilizing beads during bead washing operations. The droplet actuator device may include nucleotide base reservoirs and dedicated nucleotide base electrode paths arranged for transporting nucleotide base droplets from nucleotide base reservoirs to the reactor path. The droplet actuator device may include one or more wash buffer reservoirs associated with electrode paths arranged for transporting wash buffer droplets from wash buffer reservoirs to the reactor path. The droplet actuator device may include one or more sample reservoirs and sample paths arranged for transporting sample droplets from the one or more sample reservoirs to the reactor path. The droplet actuator device may include one or more enzyme reservoirs and dedicated enzyme electrode paths arranged for transporting enzyme droplets from the one or more enzyme reservoirs to a detection electrode.

Nucleic Acid Amplification and Sequencing on a Droplet Actuator

The invention relates to a droplet actuator with a substrate comprising electrodes arranged for conducting droplet operations on a droplet operations surface of the substrate; a filler fluid phase in contact with the droplet operations surface at least partially surrounding a droplet phase comprising a droplet arranged on one or more of the electrodes, the droplet comprising: (i) a target substance susceptible to loss from the droplet phase into the filler fluid phase; and (ii) an additive which reduces loss of the target substance to the filler fluid phase relative to a corresponding droplet not comprising the additive. The invention also relates to various compositions and methods.

Use of Additives for Enhancing Droplet Operations

The invention provides droplet actuators and droplet actuator cassettes including reagent storage capabilities, as well as methods of making and using the droplet actuators and cassettes. The invention also provides continuous flow channel elements and techniques for using electrodes to manipulate droplets in flowing streams. The invention also discloses methods of separating compounds on a droplet actuator. Various other aspects of the invention are also disclosed.

Michael G. Pollack

Papers

Surface assisted fluid loading and droplet dispensing

3-d imaging of moving droplets for microfluidics using optical coherence tomography

Nucleic Acid Amplification and Sequencing on a Droplet Actuator

Use of Additives for Enhancing Droplet Operations

Method of Loading a Droplet Actuator