A multiplexable microfluidic injector for versatile encoding of droplets

Abstract

While droplet microfluidics brings paradigm shifts in biological and chemical studies due to its unprecedented precision, throughput and cost-effectiveness, the colossal number of droplets required makes their identification and tracking a challenging task, hindering the application of droplets as individual bioreactors. Herein, we develop a multiplexable injector which exploits a distinctive design comprising a circular electrode and a concentric fluidic channel to accommodate multiple injection ports for on-demand droplet injection and encoding. Droplet ingredients can be precisely injected via pressure pulse regulation. Through varying the fluorescence in droplets, binary coding and gradient coding are successfully demonstrated with droplet sequences. Additionally, a device with three individually controllable injectors is exploited to form color-encoded droplets via various single or combinatorial injection modes. We also demonstrate that these color-coded droplets can be further collected and identified via an image analysis algorithm. As the developed platform is versatile, compact, and easy to integrate, we foresee it can potentially be used in applications such as multiplexed compound screening, combinatorial synthesis, or other multistep assays.