Volume‐Controlled Selective‐Dispensation‐Based Mixing of Multiple Solutions Using the Droplet Array Sandwiching Technology†

The droplet array sandwiching technology (DAST) is conventionally deployed to control the contact and separation of vertically opposed droplet arrays; DAST achieves material transport between the upper and lower droplets. In this DAST‐based study, we demonstrated the mixing of multiple solutions via selective dispensing (achieved via volume control based on the adjustment of the radius difference between the upper and lower droplets) and vertical manipulation of the substrate to control the distance between the upper and lower droplets. Then, we controlled droplet height using wettability patterns with precisely defined diameters through lithography. As a result, we achieved a large modulation of the droplet height (~0.35 mm) and realized three distinct droplet heights of 1.31, 1.12, and 0.96 mm. Consequently, we enabled the selective dispensing of two different dye solutions. Thus, we present a volume‐controlled selective‐dispensation‐based droplet manipulation mechanism that can be extended to large‐scale droplet arrays containing multiple reagents, advancing high‐throughput screening in biochemical analysis.