Microfluidic electrical sorting of particles based on shape in a spiral microchannel

Abstract

Shape is an intrinsic marker of cell cycle, an important factor for identifying a bioparticle, and also a useful indicator of cell state for disease diagnostics. Therefore, shape can be a specific marker in label-free particle and cell separation for various chemical and biological applications. We demonstrate in this work a continuous-flow electrical sorting of spherical and peanut-shaped particles of similar volumes in an asymmetric double-spiral microchannel. It exploits curvature-induced dielectrophoresis to focus particles to a tight stream in the first spiral without any sheath flow and subsequently displace them to shape-dependent flow paths in the second spiral without any external force. We also develop a numerical model to simulate and understand this shape-based particle sorting in spiral microchannels. The predicted particle trajectories agree qualitatively with the experimental observation.

Figure 1

Picture of the microfluidic device (the spiral microchannel is filled with green food dye for clarity) used in the particle sorting experiment. The block arrows indicate the particle moving directions during the sorting process.

Figure 2

Illustration of the shape-based particle sorting mechanism in an asymmetric double-spiral microchannel. Particles are deflected by negative C-iDEP to align near the outer wall of the first spiral and then displaced by negative C-iDEP to shape-dependent flow paths in the second spiral. Also shown are the electric field lines (equivalent to fluid stream lines with short arrows indicating the directions) and contour (background color, the darker the larger magnitude).

Figure 3

Snapshot images illustrating the continuous electrical sorting of 5 μm-diameter spherical particles and 3.5 μm-diameter/6 μm-length peanut-shaped particles in an asymmetric double-spiral microchannel by C-iDEP: (a) inlet, (b) center, and (c) trifurcation of the channel. The average DC electric field across the channel length is around 250 V/cm. Note that the peanut-shaped particles have been individually highlighted in (a) and (c) for a better illustration. The block arrows indicate the flow directions.

Figure 4

Purity test of the shape-based particle sorting by C-iDEP in terms of the percentages of spherical and peanut-shaped particles collected into outlet 1 and outlet 2 [see the labeling in Figs. 13c] of the spiral microchannel, respectively.

Figure 5

(a) The numerically predicted trajectories of spherical and peanut-shaped particles (three for each type with one showing the shape) moving electrokinetically through the most inner loop of an asymmetric double-spiral microchannel; (b) zoom-in view of the predicted translation and rotation of particles (one for each type) at the initial few time steps; (c) further zoom-in view of the distorted electric field lines and contour (the darker the larger magnitude) around a peanut-shaped particle. The block arrows in (a) indicate the flow directions.