Multiplexed fluorescence and scatter detection with single cell resolution using on-chip fiber optics for droplet microfluidic applications

Droplet microfluidics has emerged as a critical component of several high-throughput single cell analysis techniques in biomedical research and diagnostics. However, while there has been significant progress in the individual assays being developed, multi-parametric optical sensing of droplets and their encapsulated contents remains challenging. The current common approach of microscopy based high-speed imaging of droplets is technically complex and requires expensive instrumentation limiting their large-scale adoption. Here we have adapted the principles of the widely established technique of flow cytometry to a novel optofluidic setup - the OptiDrop platform, with on-chip detection of scatter and multiple fluorescence signals from microfluidic droplets and their contents using optical fibers. The highly customizable on-chip optical fiber-based signal detection system enables simplified, miniaturized, low-cost, multi-parametric sensing of optical signals with high sensitivity and single cell resolution within each droplet. Our work on differential expression analysis of the Major Histocompatibility Complex (MHC) protein in response to IFN{gamma} stimulation further demonstrates the OptiDrop platforms capabilities in sensitively detecting cell surface biomarkers using fluorescently labeled antibodies. The OptiDrop platform thus combines the versatility of flow cytometry with the power of droplet microfluidics to provide wide-ranging optical sensing solutions for research and diagnostics.