On-Demand and Size-Controlled Production of Droplets by Magnetically Driven Microtool

We have successfully produced size-controlled emulsion droplets on a chip by adjusting the vibration frequency for MMT. The novelty of this work is the fabrication of a thin coplanar Au electrode on the substrate of a microchip to work as a microsensor, and this microsensor contributed to a droplet-generation system with size estimation. When a droplet passes through the microsensor in the microchannel, it causes a change in the capacitance across a pair of microelectrodes in the microchannel, depending on the size of the droplet. We monitored the change in impedance in real time. The microsensor provided an output voltage proportional to the size of the droplet. The sensor output was observed by an oscilloscope at the primary stage. Manually we estimated the size and set a new actuation frequency for MMT to achieve on-demand and size control of the droplet. Real-time droplet detection was applied in this system. By monitoring the actuation frequency for MMT, size-controlled and on-demand droplet generation could be successfully carried out.