Figure 1.

Early observations of inertial focusing in different microfluidic geometries. (a, top left) Schematic and image of inertial focusing in an asymmetrically curved microchannel. (bottom left) Longitudinal ordering in straight channels with the spacing measured to be multiples of 3.6 times the particle diameter at the same cross-sectional equilibrium positions. ACF is an autocorrelation function used to measure the spacing or lag between particles in an image (3). (right) Particle Reynolds number (Re_P) effects in both straight and asymmetrically curved microchannels, visualized using confocal microscopy, with the reduction in the number of equilibrium positions from four to one in the curved channels. (b, top) Dean flow fractionation of two differently sized particles (purple, 1.9-μm diameter; green, 7.32-μm diameter). (Reproduced from 46 with permission from The Royal Society of Chemistry.) (bottom) Early spiral results showing focusing to half of the channel cross section in an extremely long (~2-m) spiral. (Reprinted with permission from 54. Copyright 2011, AIP Publishing LLC.) (c) Early use of expansion/contraction devices for focusing particles, showing the behavior at three positions along the device at increasing channel Reynolds number, Re_C. (Panel reprinted with permission from 68. Copyright 2008, American Chemical Society.)