Operating regimes of a magnetic split-flow thin (SPLITT) fractionation microfluidic device for immunomagnetic separation

Magnetic bead-based immunoassays in the microfluidic format have attracted particular interest as it has several advantages over other microfluidic separation techniques. Magnetic split-flow thin fractionation (SPLITT) is a compact version of microfluidic sorting where a bidispersed or polydispersed suspension of magnetic particle–analyte conjugates can be selectively isolated into co-flowing streams of nearly monodispersed particles. Although the device offers capability of identifying and separating more than one target analytes simultaneously, its performance is sensitive to the slightest variation of the operating condition. Herein, we have numerically investigated the performance of a microscale magnetic SPLITT device. Using a coupled Eulerian–Lagrangian approach, we have evaluated the capture efficiency (CE) and separation index (SI) for each particle type collected at their designated outlet of the SPLITT device and identified the best regimes of operating parameters. While the CE figures are found to be best represented by a group variable Π, the SI values are better represented as function of the product of the group variables γ and β; the SI versus Π plots clearly separate into two basic trends: one for constant β (i.e., varying γ) and the other for constant γ (i.e., varying β). Our study prescribes the desired operating regimes of a microfluidic magnetophoretic SPLITT device in a practical immunomagnetic separation application.