Droplet Tweezers Based on the Hydrophilic–Hydrophobic Interface Structure and Their Biological Application

Droplet controllable operation has wide applications in microfluidics, biomedicine, microreactors, and other fields. Droplets can spontaneously transfer from a high-energy state to a low-energy state, but how to reverse transfer the droplets is a difficult task. In this article, we use a special hydrophilic–hydrophobic interphase structure (HHIS) to achieve this reverse transfer. We specifically study the critical conditions under which droplet transfer can be achieved. The length of the hydrophilic surface in this structure and the hydrophilic/hydrophobic properties of the surface must be in the appropriate range. Based on this, an optimized structure used to transfer droplets was designed. Finally, we carried out research on biological applications and successfully achieved the transfer of droplets from zebrafish eggs and zebrafish larvae. This unique method is low-cost, biofriendly, and highly applicable to various surfaces, illustrating the great potential in chemical and biological analysis.