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There is a great demand to measure protein-ligand interactions in rapid and low cost way. Here, we developed a microfluidic droplet-based thermal shift assay (dTSA) system for high-throughput screening of small-molecule protein ligands. The system is composed of a nanoliter droplet array chip, a microfluidic droplet robot, and a real-time fluorescence detection system. Total 324 assays could be performed in parallel in a single chip with an 18 x 18 droplet array. The consumption of dTSA for each protein or ligand sample was only 5 nL (femtomole scale), which is significantly reduced by over 3 orders of magnitude compared with those in 96- or 384-well plate-based systems. We also observed the implementation of TSA in nanoliter droplet format could substantially improve assay precision with relative standard deviation (RSD) of 0.2% (n = 50), which can be ascribed to the enhanced thermal conduction in small volume reactors. The dTSA system was optimized by studying the effect of droplet volumes, as well as protein and fluorescent dye (SYPRO Orange) concentrations. To demonstrate its potential in drug discovery, we applied the dTSA system in screening inhibitors of human thrombin with a commercial library containing 100 different small molecule compounds, and two inhibitors were successfully identified and confirmed. [ABSTRACT FROM AUTHOR]

Here we developed the surface-assisted multifactor fluid segmentation (SAMFS), an automated, fast, and flexible approach for generating a two-dimensional droplet array with tunable droplet volumes, for multivolume digital polymerase chain reaction (PCR). The SAMFS was developed based on the combination of robotic liquid handling and surface-assisted droplet generation techniques, where a continuous aqueous stream that flowed out from a capillary probe was segmented and immobilized on hydrophilic micropillars of a microchip into massive oil-covered droplets with the probe rapidly scanning over the microchip. We studied various factors affecting the droplet generation process, including micropillar top area, distance between adjacent micropillars, aqueous stream flow rate, and microchip moving speed, and demonstrated a high droplet generation throughput up to 50 droplets/s and a largest droplet volume adjusting range from 0.25 to 350 nL. The SAMFS approach was adopted to form an oil-covered array of 994 droplets with four different volumes (1.2, 6, 30, and 150 nL droplets) required for multivolume digital PCR within 8 min. The droplet array system was applied in absolute quantification of plasmid DNA under the multivolume digital PCR mode with a dynamic range spanning 4 orders of magnitude, as well as measurement of HER2 expression levels in different breast cancer cell lines. The results are consistent to those obtained by quantitative real-time PCR method, while the present one has higher precision. [ABSTRACT FROM AUTHOR]