Stripped Electrode Based Electrowetting-on-Dielectric Digital Microfluidics for Precise and Controllable Parallel Microdrop Generation

Abstract

Microdrop generation with excellent controllability and volume precision is of paramount significance for a large variety of microfluidic applications. In this work, we propose a new configuration comprising only stripped electrodes of rectangular shape for the closed electrowetting-on-dielectric digital microfluidic (EWOD DMF) system and investigate its parallel microdrop generation outcomes via a numerical approach. The microfluidic droplet motion is solved by a finite-volume scheme on a fixed computational domain. The numerical model is verified by an experimental study of microdrop production from an EWOD DMF device with three different electrode designs. After model verification, we examine the influences of the equilibrium contact angle and the spacing of the microchannel on stripped electrode based microdrop generation outcomes and discover five different regimes including the phenomena of satellite droplet formation and separation cessation. Despite the various generation outcomes, the daughter droplet size is found to vary linearly with a dimensionless EWOD parameter κ*. More importantly, for all successful generations, the deviation of the daughter droplet size from that of the stripped electrode is smaller than 3.5%, which even reaches zero in proper conditions. This new configuration can be utilized as a convenient alternative for electrowetting-induced parallel microdrop production with excellent precision and controllability.

Precise Droplet Dispensing in Digital Microfluidics with Dumbbell-Shaped Electrodes

“…While almost all parameters involved in the dispensing process can affect the droplet volume, the necking process is more important than other steps based on the analysis presented above. Since the volumetric inaccuracy of droplets dispensed consecutively from the non-filling reservoir is mainly due to the uncertainty of the whereabouts of liquids during the necking and splitting process, an intuitive solution is to reduce the size of the splitting electrode to reduce the volume of this portion of liquid [ 18 , 19 ].…”

Microfluidics-Enabled Soft Manufacture of Materials with Tailorable Wettability

“…Different from closed-channel microfluidic droplet generation, EWOD digital microfluidics serves as an open-space platform for droplet manipulation, including generation, transportation, fission, and fusion. − With digital microfluidics, droplet generation is controlled by electrodes through droplet splitting and dispensing from liquid reservoirs . For example, electrodes of different sizes induce unequal droplet splitting that produces daughter droplets of different volumes, and stripped electrodes of rectangular shape enable parallel microdroplet generation . Satellite droplets are formed during droplet splitting, , which can be harnessed for generating submicroliter droplets that break down the geometry limit imposed by electrodes .…”

“…For example, electrodes of different sizes induce unequal droplet splitting that produces daughter droplets of different volumes, and stripped electrodes of rectangular shape enable parallel microdroplet generation . Satellite droplets are formed during droplet splitting, , which can be harnessed for generating submicroliter droplets that break down the geometry limit imposed by electrodes . Besides, digital microfluidics demonstrates the ability to produce two-phase droplets composed of an aqueous and an organic compartment, which is useful for acid–base workup, liquid–liquid extraction, and in-line solvent-swap …”

On-the-Fly Mass Spectrometry in Digital Microfluidics Enabled by a Microspray Hole: Toward Multidimensional Reaction Monitoring in Automated Synthesis Platforms

“…For chemical synthesis applications, 39−42 DMF is usually performed in a closed chip format where the droplets/reagents are contained between a bottom and a cover plate. 43,44 While this prevents evaporation and ensures reliable and safe handling of dissolved chemicals, it complicates the chemical analysis of the droplets that are somewhat trapped inside the chip. DMF is still in its infancy, and mostly simple optical readout methods such as visual observation, fluorescence, 45 and chemiluminescence 46 are used, or the device is dismantled to analyze the droplets offline.…”