Microfluidics: Fluid physics at the nanoliter scale

Todd M. Squires and Stephen R. Quake
Rev. Mod. Phys. 77, 977 – Published 6 October 2005

Abstract

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 Péclet 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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    DOI:https://doi.org/10.1103/RevModPhys.77.977

    ©2005 American Physical Society

    Authors & Affiliations

    Todd M. Squires*

    • Departments of Physics and Applied & Computational Mathematics, California Institute of Technology, Pasadena, California 91125, USA

    Stephen R. Quake

    • Departments of Applied Physics and Physics, California Institute of Technology, Pasadena, California 91125, USA

    • *Present address: Department of Chemical Engineering, University of California, Santa Barbara, CA 93106. Electronic address: squires@engineering.ucsb.edu
    • Present address: Department of Bioengineering, Stanford University, Stanford, CA 94305. Electronic address: quake@stanford.edu

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    Issue

    Vol. 77, Iss. 3 — July - September 2005

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