Particle separation by a moving air–liquid interface in a microchannel

Particle separation is an important topic in microfluidic field and has recently gained significant attention in sample preparations for biological and chemical studies. In this paper, a novel particle separation method was proposed. In this method, the particles were separated by the air–liquid interface in a microchannel. The motion of the air–liquid interface was controlled with a syringe pump. Depending on the air–liquid interface speed, the liquid film thickness and the viscous force on particles were changed and the particles were separated by sizes. We observed the separation of 1.01 μm particles from the larger particles when the air–liquid interface speed was less than 11 μm/s, and the separation of both 1.01 μm and 5.09 μm particles from the larger particles when the interface speed was between 11 μm/s and 120 μm/s. When the speed was higher than 120 μm/s, the drag force of the liquid flow generated by the advancing interface on particles was so strong that the flow removed all particles off from the bottom channel wall and there were no particles left behind the advancing interface.

Particle separation by size by an advancing air–liquid interface at different speed (a) at 10 μm/s, separate 1 μm particles from 5 and 10 μm particles and (b) at 35 μm/s, separate both 1 and 5 μm particles from the 10 μm particles.Figure optionsDownload high-quality image (85 K)Download as PowerPoint slideResearch highlights
► In this paper, a novel method was demonstrated to separate particles by size by using an advancing air–liquid interface in a microchannel.
► At a lower speed, small particles can be engulfed by the advancing interface while larger particles are pushed away by the interface.
► At a lower speed, the thickness of the liquid film behind the moving air–liquid interface determines what sized particles can be separated from the rest of the particles in the bulk liquid phase.
► This technique is totally independent on the electric, magnetic and optic properties of the particle and the liquid and does not required any pre-treatment of the particles such as labelling.