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This article presents a validated mathematical model of a dielectrophoresis (DEP)-based microfluidic device capable of 3D-focusing microscale entities at any lateral location inside the microchannel. The microfluidic device employs planar, independently controllable, interdigitated transducer (IDT) electrodes on either side of the microchannel. The developed model is used for understanding the influence of different geometric and operating parameters on 3D focusing, and it comprises of motion equation, Navier-Stokes equation, continuity equation, and electric potential equation (Laplace equation). The model accounts for forces associated with inertia, gravity, buoyancy, virtual mass, drag, and DEP. The model is solved using finite difference method. The findings of the study indicate that the 3D focusing possible with the proposed microfluidic device is independent of microscale entity's size and initial position, microchannel height, and volumetric flow rate. In contrast, 3D focusing achievable with the microfluidic device is dependent on the applied electric potential, protrusion width of electrodes, and width of electrode/gap. Additionally, the lateral position of 3D focused can be controlled by varying the applied electric potential. The advantage of the proposed microfluidic device is that it is simple to construct while capable of achieving 3D focusing at any lateral location inside the microchannel.

We describe the design, microfabrication, and testing of a microfluidic device for the separation of cancer cells based on dielectrophoresis. Cancer cells, specifically green fluorescent protein-labeled MDA-MB-231, are successfully separated from a heterogeneous mixture of the same and normal blood cells. MDA-MB-231 cancer cells are separated with an accuracy that enables precise detection and counting of circulating tumor cells present among normal blood cells. The separation is performed using a set of planar interdigitated transducer electrodes that are deposited on the surface of a glass wafer and slightly protrude into the separation microchannel at one side. The device includes two parts, namely, a glass wafer and polydimethylsiloxane element. The device is fabricated using standard microfabrication techniques. All experiments are conducted with low conductivity sucrose-dextrose isotonic medium. The variation in response between MDA-MB-231 cancer cells and normal cells to a certain band of alternating-current frequencies is used for continuous separation of cells. The fabrication of the microfluidic device, preparation of cells and medium, and flow conditions are detailed. The proposed microdevice can be used to detect and separate malignant cells from heterogeneous mixture of cells for the purpose of early screening for cancer.

We present the development of a dynamic model for predicting the trajectory of microparticles in microfluidic devices, employing dielectrophoresis, for Hyperlayer field-flow fractionation. The electrode configuration is such that multiple finite-sized electrodes are located on the top and bottom walls of the microchannel; the electrodes on the walls are aligned with each other. The electric potential inside the microchannel is described using the Laplace equation while the microparticles' trajectory is described using equations based on Newton's second law. All equations are solved using finite difference method. The equations of motion account for forces including inertia, buoyancy, drag, gravity, virtual mass, and dielectrophoresis. The model is used for parametric study; the geometric parameters analyzed include microparticle radius, microchannel depth, and electrode/spacing lengths while volumetric flow rate and actuation voltage are the two operating parameters considered in the study. The trajectory of microparticles is composed of transient and steady state phases; the trajectory is influenced by all parameters. Microparticle radius and volumetric flow rate, above the threshold, do not influence the steady state levitation height; microparticle levitation is not possible below the threshold of the volumetric flow rate. Microchannel depth, electrode/spacing lengths, and actuation voltage influence the steady-state levitation height.