EWOD Chip with Micro-Barrier Electrode for Simultaneous Enhanced Mixing during Transportation

Abstract

Digital microfluidic platforms have been extensively studied in biology. However, achieving efficient mixing of macromolecules in microscale, low Reynolds number fluids remains a major challenge. To address this challenge, this study presents a novel design solution based on dielectric electro-wetting (EWOD) by optimizing the geometry of the transport electrode. The new design integrates micro-barriers on the electrodes to generate vortex currents that promote mixing during droplet transport. This design solution requires only two activation signals, minimizing the number of pins required. The mixing performance of the new design was evaluated by analyzing the degree of mixing inside the droplet and quantifying the motion of the internal particles. In addition, the rapid mixing capability of the new platform was demonstrated by successfully mixing the sorbitol solution with the detection solution and detecting the resulting reaction products. The experimental results show that the transfer electrode with a micro-barrier enables rapid mixing of liquids with a six-fold increase in mixing efficiency, making it ideal for the development of EWOD devices.

Keywords: EWOD; micro-barrier; microfluidic; mixing.

Figure 1

Schematic diagram of EWOD equipment. (a) Design of electrodes with a micro-barrier. The height of the micro-barrier is H_b. The electrode array is connected to two opposite electrical signals, with the active electrode filled with purple and the opposite filled with orange. The electrodes are alternately activated, and the droplet moves to the right. Detailed design drawings are in Supplementary Information. (b) A side view of the structure of the EWOD device.

Figure 2

Internal streamline of the droplets. (a) At the end of step 1, the horizontal F_EWOD is still dominant and the streamline is mostly horizontal. At this point, the droplet starts to pass through the Barrier, and the tiny amount of F_EWOD makes the internal streamline start to bend slightly. (b) The droplet completely passes through the Barrier at this time, the horizontal and vertical F_EWOD act together, and vortices are formed inside the droplet.

Figure 3

The distribution of the dye in the droplets varies with the number of mixings or time elapsed. The initial volume of all droplets is 0.65 μL, complete process is shown in Movie S2. (a) The blue dye in DI water with Barrier EWOD Chip. (b) The blue dye in DI water with Re EWOD Chip. (c) Blue dye diffusion in DI water.

Figure 3

The distribution of the dye in the droplets varies with the number of mixings or time elapsed. The initial volume of all droplets is 0.65 μL, complete process is shown in Movie S2. (a) The blue dye in DI water with Barrier EWOD Chip. (b) The blue dye in DI water with Re EWOD Chip. (c) Blue dye diffusion in DI water.

Figure 4

Mixing degree at different times of mixing.

Figure 5

Partitioning and particle motion within a droplet. (a) The method of defining Δα, high and low speed zones. (b) The particles within the droplet rotate, and the diameter of the particles is 80 μm and H_b is 200 μm. The three colors represent three particles.

Figure 6

The effect of the barrier critical size H_b on Δα. Where L means a low-speed region and H means a high-speed region.

Figure 7

Effect of different particle sizes and different H_b values on activation velocity.

Figure 8

Detection results of different times of mixing and comparison groups.