Amorphous-to-crystalline transition strategy boosting copper-nickel bimetallic anchored hollow covalent organic framework nanozyme for colorimetric sensing of epinephrine.

Hollow covalent organic framework (HCOF) with a well-ordered pore structure can provide a robust platform for the anchoring of metal nanoparticles to design an innovative and potent nanozyme. Herein, an amorphous-to-crystalline transition strategy was utilized to synthesize the uniform HCOF, which was used as an effective nanocarrier for the anchoring of Cu-Ni bimetallic nanoparticles to prepare Cu-Ni/HCOF nanozyme with laccase-mimicking activity. By integrating the morphological control of amorphous covalent organic polymer (COP) and the crystallization-induced hollowing out, the synthesized HCOF increased the substrate enrichment and diffusion, super-adding the massive loading of Cu-Ni nanoparticles, which significantly promoted the catalytic activity. Taking advantage of the laccase-mimicking activity of the Cu-Ni/HCOF nanozyme, simple and efficient detection of epinephrine was achieved with a detection limit of 0.14 µg/mL. This colorimetric sensing strategy offered an efficient approach for epinephrine detection in a complex matrix, exhibiting potential application in the early diagnosis of disease.