Abstract
Monodisperse droplets are important in drug screening, and cell-based and biochemical research. However, conventional methods for creating droplets, such as co-flow, T-junction and flow-focusing, have poor monodispersity because of fluctuations in the flow rate. Because step emulsification is based on the principle of Laplace pressure, it is insensitive to the flow rate and yields a constant and high monodispersity. In the present study, we combine electrowetting and step emulsification to reduce the negative influence of flow-rate fluctuations and to prepare highly monodisperse droplets. We demonstrate that the flow rate and voltage applied to the droplets can independently influence the droplet size. This method has great potential in chip-based bioanalysis and cell-based studies where highly monodisperse droplets are needed.
Highlights
Lab-on-chip platforms for drug screening, cell-based studies and bioanalysis need highly monodisperse droplets for quantitative analysis
Many factors have been shown to contribute to the size of droplets produced by step emulsification, such as the surface tension, the contact angle of the dispersed fluid on the step, and the viscosity of the two phases.[9]
Because the curvature of the bulb is closely related to the contact angle, variation of the contact angle may change the time required for the droplet to be released and the droplet size
Summary
Lab-on-chip platforms for drug screening, cell-based studies and bioanalysis need highly monodisperse droplets for quantitative analysis. It is reasonable to use the contact angle as a tool to adjust the droplet size and offset the effect of fluctuations in the flow rate in step emulsification. After fabricating the device and carrying out the experiments, the figure of relationship among droplet size, flow rate and voltage applied is obtained.
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