Microdroplet event recognition and volume detection system based on flexible printed circuit electrode

Changes of microdroplet volume and the occurrence of different droplet events will exert a significant influence on droplet-based microfluidics. Droplet volume is closely related to reagent consumption and hydrodynamic resistance while droplet events reflect actual microchannel conditions. Based on current research, this work was dedicated to fabricate a reliable microdroplet sensing system with event recognition and volume detection function. Signal acquisition was on the basis of capacitance coupled detection and the coplanar fork sensing electrode was fabricated by flexible printed circuit(FPC) which was tens of times cheaper than photolithography. Wave peaks will appear while ink droplets traverse over the fork electrode from above. Shape features of waveform were used to recognize some simple droplet events and the period was employed to calculate droplet volume. Through experimental verification, droplet generation and droplet merging events could be recognized and distinguished by the system. In addition, the detection error between the theoretical volume calculated from formula and the actual volume derived from image analysis was less than 0.5 nL. The sensing system possesses the potential to achieve high throughput detection and surely can be employed to recognize more complicated droplet events in the future.