Sheath-less high throughput inertial separation of small microparticles in spiral microchannels with trapezoidal cross-section

Abstract

Various mechanisms of different designs have emerged for the purpose of microparticle separation and cell sorting. The main goals behind such designs are to create high throughput and high purity sample isolation. In this study, high efficiency, high throughput and precise separation of microparticles under inertial lift and drag forces induced by trapezoidal curvilinear channels are reported. This work is the first to focus and recover 2 from 5 μm and 2 from 10 μm particles in spiral channels in a sheath-less flow device, which reduces the overall complexity of the system and allows for higher throughput. The new microfluidic chip design is fabricated in glass using femtosecond laser ablation. In addition, mathematical force calculations were conducted during the design phase of the microfluidic channels and compared with experiments. The results show a close prediction of the equilibrium position of the tested microparticles.

Fig. 1. Trapezoidal microfluidic chip representation. (A) Fabricated spiral microfluidic chip with one inlet and two outlets, the microchannels are filled with red dye for better contrast. (B) Illustration of the spiral channel principle of operation showing a comparison between Dean vortices in rectangular and trapezoidal channel cross-sections.

Fig. 2. The fabricated trapezoidal channel investigated by 3D microscopy. (A) Three-dimensional reconstruction of the trapezoidal microchannel showing the inner and outer walls. (B) Top view of the branch at the end of the spiral shape where the red lines indicate the paths generated by the VB script to produce trapezoidal channels. (C) Channel cross-section profile as referenced in (B), showing the depth at each wall.

Fig. 3. Fluorescent green light intensity line profile (across the outlet channel) for 5 μm particles with 0.0125% (w/v) and 0.0025% (w/v) suspension concentration at 0.7 mL min⁻¹. Higher concentration values may increase the number of equilibrium positions.

Fig. 4. The 2, 5 and 10 μm fluorescent microparticle trajectories at flow rates from 0.1–1.0 mL min⁻¹. The dashed lines represent the channel's outline.

Fig. 5. The separation of 2 μm particles from 10 μm (a) at the flow rate of 1.0 mL min⁻¹, and 2 μm particles from 5 μm (b) at the flow rate of 0.6 mL min⁻¹.