Droplet manipulation on an adjustable closed-open digital microfluidic system utilizing asymmetric EWOD.

The closed-open digital microfluidic (DMF) system offers a versatile and powerful platform for various applications by combining the advantages of both closed and open structures. The current closed-open DMF system faces challenges in scaling up due to electrode structural differences between closed and open regions. Here we developed an adjustable closed-open DMF platform by utilizing the modified slippery liquid-infused porous surfaces (SLIPS) with asymmetric electrowetting on dielectric (AEWOD) as a hydrophobic dielectric layer. The consistent electrode structures of the bottom printed circuit board (PCB) electrode array on both the closed and open regions, and the utilization of a transparent acrylic with floating potential as the top plate allow a low-cost and easily scalable closed-open DMF system to be achieved. The impacts of applied voltage, parallel plate spacing, electrode switching interval, and electrode driving strategies on various droplet manipulations were investigated. The results show that the optimal plate spacings range from 340-510 μm within the closed region. Meanwhile, we also studied the influence of the thickness, geometry, and position of the top plate on the droplet movement at the closed-open boundary. Through force analysis and experimentation, it is found that a thin top plate and a bevel of ∼4° can effectively facilitate the movement of droplets at the boundary. Finally, we successfully achieved protein staining experiments on this platform and developed a customized smartphone application for the accurate detection of protein concentration. This innovative closed-open DMF system provides new possibilities for future applications in real-time biological sample processing and detection.