Triphase Interfacial Nucleation Enables Microneedle-Templated Metal–Organic Framework Coating for <i>In Situ</i> DNA Capture and Release

Organized immobilization of porous metal–organic framework (MOF) particles onto polymeric microneedle surfaces creates a thermodynamically favorable pathway for the efficient capture and enrichment of target molecules from biofluids during in situ sampling. Synthesis and surface deposition via homogeneous nucleation suffer from uncontrollable density, inferior adhesion, and substrate-damaging fabrication. To address these challenges, we propose in situ growth of MOFs on microneedles with water-based solvents under ambient conditions via a triphase interfacial heterogeneous nucleation strategy. Solvent evaporation at the gas–liquid interface enriches precursors to promote heterogeneous nucleation of MOFs on the solid polymeric template. Meanwhile, Marangoni flow continuously replenishes the liquid–solid interface with precursors for sustained lateral crystal growth and Ostwald ripening. The gas–liquid–solid phase system synergistically promotes the uniform, dense, and robust coverage of particles on the template surface, which has been validated across multiple MOF species. Harnessing the unsaturated Zr sites of UiO-66, the MOF-functionalized microneedles are demonstrated in enhancing selective DNA accommodation and elution, as well as enduring cyclic liquid immersion and plant leaf insertion. The bulk-to-interface interaction and capture transformation between microneedles and target tissues drive the advancement of on-site biosampling technologies.