Integrating Multi-Measuring-Point Fluorescence Detector for Droplet Microfluidics

Microfluidic analysis of biological samples in emulsion droplets has revolutionized high-throughput assays, including single-cell transcriptomics. Optofluidic integration and miniaturization position optical fibers close to a microfluidic channel, which carries the droplet reaction compartments. In this configuration, one optical fiber excites a fluorescence reporter in the droplet, and another detects the fluorescence emission. In principle, multiple fluorescence wavelengths can be interrogated simultaneously, but the device can analyze each droplet only once per run. We implement multiple measuring points in series to multiplex the droplet assay and also allow for quantifying reaction turnover in each droplet over time. Device masters are prototyped via two-photon lithography and replica mold microfluidic devices via soft lithography. The master includes a fluidic channel and channels for the fibers. The facets of the fibers face perpendicular to the fluidic channel. We characterized the robustness of the system and the sensitivity of each measurement point. In future work, we will pursue on-chip integration towards optofluidic integrated devices for multiplexed droplet analysis.