Droplet microfluidics has become a powerful tool in many biological and clinical applications to high-throughput encapsulate reactions with single-cell and single-molecular resolutions. Microfluidic chips, such as flow-focusing droplet generators, have become commonplace in microfluidic laboratories. However, the expensive and precision-demanding microfabrication hinders their widespread use in many biomedical laboratories and clinical facilities. Herein, we present a versatile chip-free droplet generator, termed as OsciDrop, for on-demand generating size-tunable droplets with high uniformity. OsciDrop segments the fluid flowing out of the orifice of a micropipette tip into droplets by oscillating the tip under the surface of a continuous oil phase. We investigated the factors influencing droplet generation by examining several control parameters. Results show that flow rate, oscillating amplitude, and frequency are key parameters to on-demand generate monodisperse droplets. Flexible, repeatable droplet generation by OsciDrop was successfully achieved. Importantly, using an optimal asymmetrical oscillation waveform, OsciDrop can controllably generate monodisperse droplets spanning a wide volume range (200 pL - 2 μL). To demonstrate the capability of OsciDrop for chip-free droplet assays, a digital loop-mediated isothermal amplification (dLAMP) was performed to absolutely quantify African swine fever virus (ASFV) DNA templates. The OsciDrop method opens up a feasible and versatile avenue to perform droplet-based assays, exhibiting full accessibility for chip-free droplet microfluidics.
Droplet-assisted electrospray phase separation using an integrated silicon microfluidic platform
