High-Efficiency Small Sample Microparticle Fractionation on a Femtosecond Laser-Machined Microfluidic Disc

Abstract

The fabrication and testing of microfluidic spinning compact discs with embedded trapezoidal microchambers for the purpose of inertial microparticle focusing is reported in this article. Microparticle focusing channels require small features that cannot be easily fabricated in acrylic sheets and are complicated to realize in glass by traditional lithography techniques; therefore, the fabrication of microfluidic discs with femtosecond laser ablation is reported for the first time in this paper. It could be demonstrated that high-efficiency inertial focusing of 5 and 10 µm particles is achieved in a channel with trapezoidal microchambers regardless of the direction of disc rotation, which correlates to the dominance of inertial forces over Coriolis forces. To achieve the highest throughput possible, the suspension concentration was increased from 0.001% (w/v) to 0.005% (w/v). The focusing efficiency was 98.7% for the 10 µm particles and 93.75% for the 5 µm particles.

Keywords: femtosecond laser; microfluidic disc; microfluidics; microparticle separation.

Figure 1

Three-dimensional (3D) illustration of the spinning system with all its components, and the microfluidic design of the focusing channel. Microchambers are implemented along one side of the focusing channel to enhance particle focusing.

Figure 2

A 3D reconstruction of the fabricated channel showing the difference in surface roughness before and after the glass etching process. The arithmetic average values for the roughness profile ($R_a$) are 0.6755 µm and 0.4571 µm before and after glass etching, respectively.

Figure 3

Dyed deionized (DI) water flow experiment inside the focusing channel. Picture (a) shows the fluid stopping at the channel inlet due to the pressure barrier caused by the width expansion, while picture (b) is taken after rotating the microfluidic disc at 1500 rpm.

Figure 4

(a) 3D representation of the design with an illustration of forces affecting a fluid element passing through the channel. The channel size is exaggerated for demonstration purposes. (b) A cross-section in a rectangular spiral microchannel showing the direction of Dean vortices and the forces affecting microparticles flowing in that channel.

Figure 5

5 and 10 µm particles focusing results at 0.001% (w/v) and 0.005% (w/v) suspension concentrations. (a) Outlet chambers after particle fractionation experiments. (b) The effect of particle suspension concentration on focusing efficiency for 5 µm particles (left) and 10 µm particles (right). Results show that higher concentrations return higher throughput while approximately maintaining the same focusing efficiency.