Sp‐Carbon–Based Single‐Atom/Nanocluster Laccase‐Mimetic Nanozyme With Three‐Dimensional Separated Active Sites for Regulating Lignin Biosynthesis in Salt‐Stressed Maize Roots

ABSTRACT Most laccase‐mimetic nanozymes fail to replicate the synergistic, division‐of‐labor catalysis of natural multicopper laccases, limiting activity gains. A key bottleneck lies in the construction of atomically defined and spatially organized active sites that integrate oriented structural motifs with multistate electronic configurations. Here, we report a graphdiyne‐derived Cu single‐atom/nanocluster nanozyme (CCG) in which the sp‐carbon scaffold hierarchically organizes Cu single atoms (SAs) and nanoclusters (NCs) to mimic the asymmetric microenvironment and electronic structure of native laccase active sites. Cu SAs serve as electron transfer centers, while Cu NCs reproduce the oxygen‐accepting characteristics of multinuclear Cu sites. Electronic structure analyses reveal that the sp‐carbon precisely modulates Cu coordination geometries and spin states, generating tri‐site electronic features analogous to the T1/T2/T3 ensemble in natural laccases. Steady‐state kinetics reveal that CCG exhibits 5.21‐fold higher specific activity than ZmLac3 with enhanced substrate affinity. In salt‐stressed maize seedlings, CCG functionally compensated for endogenous ZmLac3 and regulated lignin biosynthesis, increasing root lignin content and cell wall thickness by 27.6% and 47.7%, and improving root activity and biomass by 61.2% under 300 mM NaCl. This study establishes an atomic‐precision design paradigm that integrates hierarchical site construction with multistate electronic coordination, guiding the development of next‐generation high‐performance biomimetic nanozymes.