Bidirectional and Stepwise Rotation of Cells and Particles Using Induced Charge Electroosmosis Vortexes.

The rotation of cells is of significant importance in various applications including bioimaging, biophysical analysis and microsurgery. Current methods usually require complicated fabrication processes. Herein, we proposed an induced charged electroosmosis (ICEO) based on a chip manipulation method for rotating cells. Under an AC electric field, symmetric ICEO flow microvortexes formed above the electrode surface can be used to trap and rotate cells. We have discussed the impact of ICEO and dielectrophoresis (DEP) under the experimental conditions. The capabilities of our method have been tested by investigating the precise rotation of yeast cells and K562 cells in a controllable manner. By adjusting the position of cells, the rotation direction can be changed based on the asymmetric ICEO microvortexes via applying a gate voltage to the gate electrode. Additionally, by applying a pulsed signal instead of a continuous signal, we can also precisely and flexibly rotate cells in a stepwise way. Our ICEO-based rotational manipulation method is an easy to use, biocompatible and low-cost technique, allowing rotation regardless of optical, magnetic or acoustic properties of the sample.

Bipolar Electrode-based Sheath-Less Focusing and Continuous Acoustic Sorting of Particles and Cells in an Integrated Microfluidic Device.

Sheath-less focusing and sorting of cells or particles is an important preprocessing step in a variety of biochemical applications. Most of the previous sorting methods depend on the use of sheath flows to realize efficient cell focusing. The sheath flow dilutes the sample and requires precise flow control via additional channels. We, for the first time, reported a method of bipolar electrode (BPE)-based sheath-less focusing, switching, and tilted-angle standing surface acoustic wave-based sorting of cells and particles in continuous flow. The device consists of a piezoelectric substrate with a pair of BPEs for focusing and switching, and a pair of interdigitated transducers for cell sorting. Smaller cells experience a weak acoustic force and reach the lower outlet, whereas larger cells are subjected to a strong acoustic force such that they are propelled toward the upper outlet. We first validate the device functionality by sorting 5 and 8 µm PS beads with a high sorting efficiency. The working and deflection regions were increased by propelling the particle beam toward the bottom edge of BPE via changing the applied voltage of BPE, further improving the sorting performance with high efficiency (94%) and purity (92%). We then conducted a verification for sorting THP-1 and yeast cells, and the efficiency and purity reached 90.7 and 91.5%, respectively. This integrated device eliminates the requirement of balancing the flow of several sheath inlets and provides a robust and unique approach for cell sorting applications, showing immense promise in various applications, such as medical diagnosis, drug delivery, and personalized medicine.

Three-dimensional rotation of deformable cells at a bipolar electrode array using a rotating electric field.

Three-dimensional rotation of cells is imperative in a variety of applications such as biology, medicine, and chemistry. We report for the first time a versatile approach for executing controllable 3D rotation of cells or particles at a bipolar electrode (BPE) array using a rotating electric field. The versatility of this method is demonstrated by 3D rotating various cells including yeast cells and K562 cells and the cells can be rotated to a desired orientation and immobilized for further operations. Our results demonstrate how electrorotation torque, induced charge electroosmosis (ICEO) flow and dielectrophoresis can be exerted on certain cells for modulating the rotation axis, speed, and direction. ICEO-based out-of-plane rotation is capable of rotating various cells in a vertical plane regardless of their shape and size. It can realize cell orientation by rotating cells toward a specific angle and enable cell rotation by steadily rotating multiple cells at a controllable speed. The rotation spectrum for in-plane rotation is further used to extract the cellular dielectric properties. This work offers a flexible method for controllable, contactless and precise rotation of different cells or particles, offering a rapid, high-throughput, and nondestructive rotation method for cell analysis and drug discovery.

Label free and high-throughput discrimination of cells at a bipolar electrode array using the AC electrodynamics.

BACKGROUND: Cell characterization and manipulation play an important role in biological and medical applications. Cell viability evaluation is of significant importance for cell toxicology assay, dose test of anticancer drugs, and other biochemical stimulations. The electrical properties of cells change when cells transform from healthy to a pathological state. Current methods for evaluating cell viability usually requires a complicated chip and the throughput is limited. RESULTS: In this paper, a bipolar electrode (BPE) array based microfluidic device for assessing cell viability is exploited using AC electrodynamics. The viability of various cells including yeast cells and K562 cells, can be evaluated by analyzing the electro-rotation (ROT) speed and direction of cells, as well as the dielectrophoresis (DEP) responses of cells. Firstly, the cell viability can be identified by the position of the cell captured on the BPE electrode in terms of DEP force. Besides, cell viability can also be evaluated based on both the cell rotation speed and direction using ROT. Under the action of travelling wave dielectric electrophoresis force, the cell viability can also be distinguished by the rotational motion of cells on bipolar electrode edges. SIGNIFICANCE: This study demonstrates the utility of BPEs to enable scalable and high-throughput AC electrodynamics platforms by imparting a flexibility in chip design that is unparalleled by using traditional electrodes. By using BPEs, our proposed new technique owns wide application for cell characterization and viability assessment in situ detection and analysis.