Mixing Mechanism of Microfluidic Mixer with Staggered Virtual Electrode Based on Light-Actuated AC Electroosmosis

In this paper, we present a novel microfluidic mixer with staggered virtual electrode based on light-actuated AC electroosmosis (LACE). We solve the coupled system of the flow field described by Navier–Stokes equations, the described electric field by a Laplace equation, and the concentration field described by a convection–diffusion equation via a finite-element method (FEM). Moreover, we study the distribution of the flow, electric, and concentration fields in the microchannel, and reveal the generating mechanism of the rotating vortex on the cross-section of the microchannel and the mixing mechanism of the fluid sample. We also explore the influence of several key geometric parameters such as the length, width, and spacing of the virtual electrode, and the height of the microchannel on mixing performance; the relatively optimal mixer structure is thus obtained. The current micromixer provides a favorable fluid-mixing method based on an optical virtual electrode, and could promote the comprehensive integration of functions in modern microfluidic-analysis systems.

Dynamic-coupling analyses of cells localization by the negative dielectrophoresis

Negative dielectrophoresis is widely used in cell localization for long-term observations such as the impedance analysis, in vivo drug screening, and cell patterns. However, the coupling effect of AC electrokinetics, including negative dielectrophoresis, AC electroosmosis, and electrothermal flow is still unclear. This work investigated cell localization based on the dynamic-coupling of dielectrophoresis, AC electroosmosis, and electrothermal flow. A two-dimensional finite element model that consisted of interdigitated array electrodes was established. The effects of system parameters on the capture efficiency were investigated, when the medium conductivity was in the range of 0.001–1 S/m. The selection of the medium conductivity is suggested to be the first step of the experiment design. Then, the choice of AC frequency and AC amplitude requires balancing the effects of transmembrane potential and temperature rise on cell viability. Besides, particular electrode spacing is evidenced to be only efficient for a specific cell diameter. Thus, the electrode spacing of the microfluidic chip needs to be optimized according to the cell's diameter.

AC Electroosmosis Effect on Microfluidic Heterogeneous Immunoassay Efficiency

A heterogeneous immunoassay is an efficient biomedical test. It aims to detect the presence of an analyte or to measure its concentration. It has many applications, such as manipulating particles and separating cancer cells from blood. The enhanced performance of immunosensors comes down to capturing more antigens with greater efficiency by antibodies in a short time. In this work, we report an efficient investigation of the effects of alternating current (AC) electrokinetic forces such as AC electroosmosis (ACEO), which arise when the fluid absorbs energy from an applied electric field, on the kinetics of the antigen–antibody binding in a flow system. The force can produce swirling structures in the fluid and, thus, improve the transport of the analyte toward the reaction surface of the immunosensor device. A numerical simulation is adequate for this purpose and may provide valuable information. The convection–diffusion phenomenon is coupled with the first-order Langmuir model. The governing equations are solved using the finite element method (FEM). The impact of AC electroosmosis on the binding reaction kinetics, the fluid flow stream modification, the analyte concentration diffusion, and the detection time of the biosensor under AC electroosmosis are analyzed.