High Throughput Digital Droplet ELISA for Ultrasensitive Multiplexed Diagnostics

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Abstract: Digital assays — in which ultra-sensitive molecular measurements are made by performing millions of parallel experiments in picoliter droplets — have generated much recent enthusiasm due to their single molecule resolution of RNA, DNA, and proteins, and their robustness to reaction conditions. These assays have enormous untapped potential for point of care disease diagnostics, but are currently mainly confined to laboratory settings due to the cumbersome instrumentation necessary to generate, control, and measure tens of millions of independent droplets. To overcome this challenge, we propose a hybrid microelectronic / microfluidic chip to `unlock' droplet-based assays for clinical use. Our microdroplet megascale detector (µMD) can generate and detect the fluorescence of millions of droplets per second (1000× faster than existing digital approaches), while achieving a 1000x greater sensitivity than conventional ELISA, using only a conventional cell phone camera. The key innovation of our approach is borrowed from the telecommunications industry, wherein we modulate the 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. To demonstrate the power of our approach, we focus our attention on the diagnosis of pancreatic cancer.