Multicolor detection of fluorescent droplets on a cell phone using time domain encoded optofluidics

Digital droplet assays - in which biological samples are compartmentalized into millions of femtoliter volume droplets and interrogated individually - have generated enormous enthusiasm for their ability to robustly detect nucleic acids and proteins with single molecule sensitivity. A key challenge in the field however has been the cumbersome instrumentation necessary to generate, process, and detect millions of individual droplets. We have demonstrated the miniaturization of droplet diagnostics into a portable platform that can process millions of droplets per second by combining the parallelization of thousands of microfluidic droplet generators onto a single chip and a strategy to rapidly detect droplets using time-domain encoded cell phone imaging. Building on our work in this area, we show that multiple fluorescent dyes can be detected in each individual droplet by encoding the excitation light from multiple LEDs with unique maximum length sequences that are decoded using cloud-based computation. By developing a strategy to carry out multiplexed digital droplet assays in a portable platform at a rate (10
⁶
droplets / sec), 1000x faster than conventional approaches on a cell phone based device, we have demonstrated a key step towards translating the sensitivity of digital assays from research laboratories to portable molecular diagnostics.