Photoresponsive Liquid Grippers for Multi-Dimensional Droplet Manipulation

Droplet manipulation has significant value in a wide range of areas, such as microfluidics, medical diagnosis, and detection. However, high-precision droplet manipulation with arbitrary control on an open surface still poses a substantial challenge, particularly in 3D droplet manipulation. Here, we propose a bilayer photoresponsive liquid gripper (PLG), which integrates an "adhesive layer" and an "actuation layer" to enable sustainable capture and release for precise 3D droplet manipulation of high-viscosity fluids (e.g., blood, serum, and pH solutions). The "adhesive layer" featuring a superhydrophobic microarrayed polydimethylsiloxane surface allows nondestructive droplet capture. Meanwhile, the "actuation layer" leverages the photo-induced bending of photodeformable crosslinked liquid crystal polymers to release the droplet without altering its surface wettability. Moreover, by simply adjusting the microstructures of its surface, PLG allows the selective capture of droplets of particular sizes, providing a new tool for droplet screening. Biochemical reactions, including blood detection, neutralization reactions, and immunoassays, are successfully demonstrated via the PLG system, underscoring its utility as an effective and versatile platform for complex droplet manipulation, biological analysis, and routine biochemical investigations.