A centrifugal force-based serpentine micromixer (CSM) on a plastic lab-on-a-disk for biochemical assays

In this paper, a centrifugal force-based serpentine micromixer (CSM) on a plastic lab-on-a-disk (LOD) for biochemical assay was designed, fabricated, and fully characterized with numerical and experimental methods. The CSM comprised two inlets, an outlet, and a serpentine microchannel composed of five circumferential channels with connecting radial channels in one layer. The centrifugal force induced in the rotating disk thoroughly mixed the sample and reagent together throughout the serpentine microchannel of the CSM. Despite its simple geometry, effective mixing performance was achieved inside the CSM because of transverse secondary flows and the three-dimensional stirring effect in the microchannel. Numerical simulation showed that the interfaces of the two streams inside the circumferential microchannel were efficiently stirred by the induced transversal velocity field. The plastic LOD was fabricated by CNC-micromilling on one layer of the thermoplastic substrate, followed by thermal bonding with a cover plastic substrate. Mixing performance of the CSM was also investigated experimentally by means of colorimetric analysis using phenolphthalein. High levels of distributive mixings were obtained within a short required mixing length. As a proof-of-concept example, a biochemical assay of albumin level was successfully determined with the help of the LOD containing the CSM. Owing to the mass-producible simple geometry, excellent mixing performance, and convenience, the CSM can be applied to biochemical assays based on the centrifugal microfluidics.