Abstract
High throughput particle/cell concentration is crucial for a wide variety of biomedical, clinical, and environmental applications. In this work, we have proposed a passive spiral microfluidic concentrator with a complex cross-sectional shape, i.e., a combination of rectangle and trapezoid, for high separation efficiency and a confinement ratio less than 0.07. Particle focusing in our microfluidic system was observed in a single, tight focusing line, in which higher particle concentration is possible, as compared with simple rectangular or trapezoidal cross-sections with similar flow area. The sharper focusing stems from the confinement of Dean vortices in the trapezoidal region of the complex cross-section. To quantify this effect, we introduce a new parameter, complex focusing number or CFN, which is indicative of the enhancement of inertial focusing of particles in these channels. Three spiral microchannels with various widths of 400 µm, 500 µm, and 600 µm, with the corresponding CFNs of 4.3, 4.5, and 6, respectively, were used. The device with the total width of 600 µm was shown to have a separation efficiency of ~98%, and by recirculating, the output concentration of the sample was 500 times higher than the initial input. Finally, the investigation of results showed that the magnitude of CFN relies entirely on the microchannel geometry, and it is independent of the overall width of the channel cross-section. We envision that this concept of particle focusing through complex cross-sections will prove useful in paving the way towards more efficient inertial microfluidic devices.
Highlights
Concentrating cells and particles has long been regarded as an essential pre-treatment step in biomedical microanalysis, clinical diagnosis, and environmental applications [1,2]
This difference in lateral positions of particles with varying sizes is further amplified upon introducing a trapezoidal cross-section which is able to separate polymorphonuclear leukocytes (PMNs) and mononuclear leukocytes (MNLs) from diluted human blood with efficiency >80% [22]
We have shown our spiral microchannel with complex cross-sectional shape is capable of overcoming challenges associated with confinement ratio (CR) > 0.07 to achieve tight focusing bands
Summary
Concentrating cells and particles has long been regarded as an essential pre-treatment step in biomedical microanalysis, clinical diagnosis, and environmental applications [1,2]. In 2014, Martel and Toner proposed a non-dimensional factor defined as the ratio of lift forces to Dean drag force, Rf, to characterize the inertial focusing flows in curved channels [21] This difference in lateral positions of particles with varying sizes is further amplified upon introducing a trapezoidal cross-section which is able to separate polymorphonuclear leukocytes (PMNs) and mononuclear leukocytes (MNLs) from diluted human blood with efficiency >80% [22]. We introduce a passive spiral microfluidic device with a complex cross-section for high-throughput particle concentration using the Dean drag force coupled with the inertial microfluidics phenomenon. Our findings provide new insight into the fabricating inertial microchannel with complex cross-sections to be widely employed as a concentration tool in the areas of environmental analysis and disease diagnosis
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