Buoyancy-Free Janus Microcylinders as Mobile Microelectrode Arrays for Continuous Microfluidic Biomolecule Collection within a Wide Frequency Range: A Numerical Simulation Study

Abstract

We numerically study herein the AC electrokinetic motion of Janus mobile microelectrode (ME) arrays in electrolyte solution in a wide field frequency, which holds great potential for biomedical applications. A fully coupled physical model, which incorporates the fluid-structure interaction under the synergy of induced-charge electroosmotic (ICEO) slipping and interfacial Maxwell stress, is developed for this purpose. A freely suspended Janus cylinder free from buoyancy, whose main body is made of polystyrene, while half of the particle surface is coated with a thin conducting film of negligible thickness, will react actively on application of an AC signal. In the low-frequency limit, induced-charge electrophoretic (ICEP) translation occurs due to symmetric breaking in ICEO slipping, which renders the insulating end to move ahead. At higher field frequencies, a brand-new electrokinetic transport phenomenon called “ego-dielectrophoresis (e-DEP)” arises due to the action of the localized uneven field on the inhomogeneous particle dipole moment. In stark contrast with the low-frequency ICEP translation, the high-frequency e-DEP force tends to drive the asymmetric dipole moment to move in the direction of the conducting end. The bidirectional transport feature of Janus microspheres in a wide AC frequency range can be vividly interpreted as an array of ME for continuous loading of secondary bioparticles from the surrounding liquid medium along its direction-controllable path by long-range electroconvection. These results pave the way for achieving flexible and high-throughput on-chip extraction of nanoscale biological contents for subsequent on-site bioassay based upon AC electrokinetics of Janus ME arrays.

Trajectories and Forces in Four-Electrode Chambers Operated in Object-Shift, Dielectrophoresis and Field-Cage Modes—Considerations from the System’s Point of View

“…Up to now, it has been shown that the LMEP approach works for the electroorientation of ellipsoidal objects [8], for DEP in multiple electrode configurations and for the calculation of mirror charge-induced forces [1,2,9]. For example, LMEP modeling of AC-electrokinetic effects can be extended to nonspherical objects, multibody systems, or Janus particles [28] to compute combined orientation, translation, and aggregation patterns [14,16,20]. Other examples include objects inducing attractive mirror charges on flat electrode surfaces and pointed electrodes inducing mirror charges in large objects.…”

Dielectrophoretic characterization and selection of non-spherical flagellate algae in parallel channels with right-angle bipolar electrodes

“…When an external electric field is applied, the prolate lossless dielectric particles prefer to align their long axes parallel to the electric field direction under the action of electro-orientation torque. Assuming that the distance between a certain point on the cell surface and the origin of the coordinate system is r under the action of DEP force, the electro-orientation moment on the non-spherical algae can be expressed as: τ orient = ∮( T̃ c − T̃ m )· r · n d A The stress tensor of fluid action on non-spherical algae is: 46 Under this circumstance, the action of fluid on non-spherical algae can be expressed as: F fluid = ∮ P̃ · n d A The rotational torque generated by the non-spherical algae due to the action of the fluid is: τ fluid = ∮ P̃ · r · n d A The moment of inertia of non-spherical algae can be expressed as: M = ∫∫∫ ρ · r 2 · n d V Therefore, the rotational angular acceleration of the non-spherical algae can be expressed as:…”

Editorial on the Special Issue on Microelectrode Arrays and Application to Medical Devices

“…In another study on electrokinetics, the transient motion of Janus particles acting as mobile microelectrodes was studied by Liu et al [ 8 ]. A Janus particle is a type of particle that has a nonuniform polarizable body, such that half of its body is less polarizable than the surrounding liquid, while the other half is more polarizable.…”

“…In this editorial note, we briefly review the major findings of the 10 articles published in the Special Issue on microelectrode arrays and application to medical devices. The articles are categorized into three sections, i.e., fabrication techniques [ 1 , 2 , 3 , 4 ], application demonstration [ 5 , 6 , 7 , 8 ], and review of recent advances in this field [ 9 , 10 ].…”