EWODbased

EWOD-based systems refer to digital microfluidic platforms that manipulate droplets on a planar array of electrodes using electric fields across a dielectric layer. By locally altering the wettability of a droplet’s contact surface, these systems can move, merge, split, and mix droplets, enabling programmable fluid handling on a compact chip.

Principle and construction: When a voltage is applied between an electrode and a counterelectrode through a thin dielectric layer and a hydrophobic coating, the droplet’s contact angle decreases at the energized site, increasing wettability. This effect, described by the Lippmann–Young relation, allows sequential activation of neighboring electrodes to transport a droplet across the array. A typical EWOD device comprises patterned conductive electrodes (often ITO or metal), a dielectric layer, and a hydrophobic top coating, with choices between open and closed configurations. Control electronics govern the electrode addressing and timing.

Operations and configurations: Open EWOD presents droplets directly on the surface, while closed EWOD sandwiches the fluid between two plates, offering improved containment. Droplet operations include translation across the array, coalescence with other droplets, splitting, and in-situ mixing or heating. Volumes are generally in the nanoliter to microliter range, and operation can be tailored for rapid, automated assays or sample preparation workflows.

Applications and limitations: EWOD-based platforms are used in lab-on-a-chip and point-of-care diagnostics, chemical synthesis, environmental monitoring, and cellular analysis. Advantages include low reagent consumption, rapid actuation, and flexible reconfigurability. Limitations involve the need for insulating dielectric layers, relatively high driving voltages, potential electrolysis or heating, evaporation, and material compatibility issues. Ongoing research aims to improve materials, reduce power, and integrate sensing and on-chip analysis.