Development of three-dimensional integrated microchannel-electrode system to understand the particles' movement with electrokinetics

Abstract

An optical transparent 3-D Integrated Microchannel-Electrode System (3-DIMES) has been developed to understand the particles' movement with electrokinetics in the microchannel. In this system, 40 multilayered electrodes are embedded at the 2 opposite sides along the 5 square cross-sections of the microchannel by using Micro Electro-Mechanical Systems technology in order to achieve the optical transparency at the other 2 opposite sides. The concept of the 3-DIMES is that the particles are driven by electrokinetic forces which are dielectrophoretic force, thermal buoyancy, electrothermal force, and electroosmotic force in a three-dimensional scope by selecting the excitation multilayered electrodes. As a first step to understand the particles' movement driven by electrokinetic forces in high conductive fluid (phosphate buffer saline (PBS)) with the 3-DIMES, the velocities of particles' movement with one pair of the electrodes are measured three dimensionally by Particle Image Velocimetry technique in PBS; meanwhile, low conductive fluid (deionized water) is used as a reference. Then, the particles' movement driven by the electrokinetic forces is discussed theoretically to estimate dominant forces exerting on the particles. Finally, from the theoretical estimation, the particles' movement mainly results from the dominant forces which are thermal buoyancy and electrothermal force, while the velocity vortex formed at the 2 edges of the electrodes is because of the electroosmotic force. The conclusions suggest that the 3-DIMES with PBS as high conductive fluid helps to understand the three-dimensional advantageous flow structures for cell manipulation in biomedical applications.

FIG. 1.

3-D Integrated Microchannel-Electrode System (3-DIMES), (a) the 3-DIMES is composed of a microchannel integrated with platinum multilayered electrodes, a printed circuit board (PCB) pin connectors, and a holder. (b) The microchannel has three inlets, three outlets, and a main flow channel. (c) The schematic diagram of the main flow channel.

FIG. 2.

Micro computed tomography (μCT) images of the 3-DIMES with square cross-sections.

FIG. 3.

Fabrication process of the 3-DIMES with integrated multilayered electrodes.

FIG. 4.

Experimental setup. (a) The 3-DIMES was placed along the gravity direction to make the main flow channel along the opposite direction of the x-component to eliminate the gravity influence on the particles' movement in the y-z plane in the cross-sections of the main flow channel; (b) one of the two electrodes (red one) is used for current injection, and another (black one) for the grounding; (c) observed cross-sections by optical microscope at different depths of y/L_y and z/L_z.

FIG. 5.

Time mean velocity vectors u_p obtained at x′-y′ plane at various depth z/L_z in Fig. 4(c) in the case of deionized water.

FIG. 6.

Time-mean velocity vectors u_p measured at x′-y′ plane at various depth z/L_z in Fig. 4(c) in the case of PBS.

FIG. 7.

x and y-components of the time-mean velocity vectors u_px and u_py in the case of PBS. (a) The time-mean velocity vectors u_px measured at y/L_y = 0.3 of x″-z″ plane at various depth z/L_z. (b) The time-mean velocity vectors u_px measured at y/L_y = 0.6 of x″-z″ plane at various depth z/L_z. (c) The time-mean velocity vectors u_py measured at y/L_y = 0.3 of x″-z″ plane at various depth z/L_z. (d) The time-mean velocity vectors u_py measured at y/L_y = 0.6 of x″-z″ plane at various depth z/L_z. (e) and (f) The comparison of u_px and u_py at various depth y/L_y and z/L_z.

FIG. 8.

Theoretical explanation of the experimental results of 3-D particle velocities for water and PBS. (a) Theoretical comparison of velocities due to different electrokinetic forces. (b) and (c) Qualitative analysis of particles' movement in x′-y′ and x″-z″ plane, dominant velocities are determined by the theoretical calculations in Table II as u_TB and u_ET.

FIG. 9.

Particle and fluid movement by electrokinetics under AC electric field, corresponding to 4 kinds of velocities.