Enzyme Catalysis Induced Nanocluster Assembly into Micrometer-Size Monolayered Nanosheets with Enhanced Near-Infrared Region II Emission

Two-dimensional (2D) nanomaterials have attracted considerable attention across diverse research fields owing to their unique physicochemical properties; however, achieving the controllable fabrication of freestanding 2D nanosheets through a template-free method under physiological conditions remains challenging. Here, an enzyme catalysis induced nanocluster assembly (ECINA) was proposed to fabricate freestanding micrometer-sized 2D nanosheets using peptide-capped gold nanoclusters (AuNCs) under mild aqueous conditions. An alkaline phosphatase (ALP)-cleavable peptide (Y P FTEFCC) was designed and utilized as a ligand for the preparation of gold nanoclusters (Y P F-AuNCs). Upon ALP catalysis, dephosphorylation induced peptide assembly and further lined up the nanoclusters, resulting in monolayered nanosheets with enhanced near-infrared-II (NIR-II) emission. Systematic investigations revealed that the assemble peptide sequence and presence of nanocluster as cores were indispensable for 2D nanosheet construction, while the types of nanoclusters were well tolerated, where copper nanoclusters (Y P F-CuNCs) afforded similar patterns under the same assembly paradigm. Importantly, overexpressed endogenous ALP could also trigger the in situ assembly of Y P F-AuNCs, allowing enhanced cellular uptake and prolonged high-contrast NIR-II imaging. This work establishes a pioneering perspective for enzyme-triggered nanocluster assembly, guiding the formation of hierarchical nanostructures in a template-free manner.