Abstract

Ultra-High Throughput Detection (> 1 million droplets / sec) of Fluorescent Droplets Using a Cell Phone Camera and Time Domain Encoded Optofluidics

Venkata Yelleswarapu, Research Scientist, University of Pennsylvania

Droplet-based assays — in which molecular measurements are made by performing millions of parallel experiments in picoliter droplets — have generated enthusiasm due to their single molecule resolution and robustness to reaction conditions. These assays have untapped potential for point-of-care diagnostics but are currently confined to laboratory settings due to the bulky instrumentation necessary to serially generate, control, and measure tens of millions of droplets. To address this challenge, we have developed the microdroplet Megascale Detector (microMD) which can generate and detect the fluorescence of millions of droplets per second (1000x faster than conventional approaches) using only a conventional cell-phone camera. The key innovation of our approach is the modulation of excitation light with a pseudorandom sequence that enables individual droplets to be resolved that would otherwise overlap due to the limited frame rate of digital cameras. Using this approach, the microMD measures droplets at a rate of 10^6 droplets / sec in 120 parallel microfluidic channels and achieves a limit of detection of 1microM rhodamine dye, sufficient for conventional droplet based assays. By miniaturizing and integrating droplet based diagnostics into a handheld format, the microMD platform can transforms droplet assays into a self-contained platform for practical use in clinical settings.