Application of Droplet-Array Sandwiching Technology to Click Reactions for High-Throughput Screening.

High-throughput screening (HTS) is an essential process in drug discovery, requiring platforms that ensure reagent economy, high efficiency, and resistance to cross-contamination. Click chemistry is well suited for HTS because of its biocompatibility, high selectivity, and quantitative fluorescent readout. We focus on droplet-array sandwiching technology (DAST), in which two droplet microarrays (DMAs) are vertically opposed to achieve solute transport and reagent mixing by controlled contact and separation. Herein, we integrate click chemistry with DAST and evaluate its feasibility as a HTS platform. In DAST, DMAs are formed on wettability-patterned (WP; hydrophilic/hydrophobic) substrates, preserving resistance to cross-contamination. First, we immobilized dibenzocyclooctyne (DBCO) on a WP substrate and verified the occurrence of DBCO-azide reaction using an azide-functional fluorescent dye. The fluorescence intensity increased with concentration and reached a plateau at higher concentrations, indicating saturation behavior in the DBCO-azide click reaction. Second, acoustic mixing with repeated droplet contact-separation was applied to generate concentration gradients on a single substrate while maintaining droplet independence. Third, we qualitatively reproduced the expected concentration dependence of manual handling by combining DAST-based gradient formation with click reaction fluorescence readout. These results reveal that DAST enables a reagent-efficient, cross-contamination-resistant, and low-instrument-dependent HTS foundation for click-chemistry-based assays.