Enhancing the peroxidase-mimicking activity of hemin by covalent immobilization in polymer nanogels

The encapsulation of catalytic active centers into polymer hydrogels represents a simple and effective strategy for enzyme mimicry. Current methods only enable the preparation of macroscopic enzyme carriers, which are far from natural enzymes in terms of their sizes, local chemical and physical properties, and catalytic activities. In this work, a nanogel strategy to immobilize hemin, a mimic of the active center for horseradish peroxidase (HRP), into a polyacrylamide (PAAm) matrix is demonstrated. Hemin was modified using N-(3-aminopropyl) methacrylamide hydrochloride (APMA) and the modified hemin together with excess APMA were covalently incorporated into PAAm nanogels. The resulting Hem@Gel shows enhanced catalytic activity and environmental tolerance compared with hemin and unmodified nanogel Hem/Gel, which has been demonstrated via the catalytic oxidation of various organic dyes. Further characterization and molecular simulations reveal the Fe–N coordination between the pendant groups and the enrichment of dye molecules and H2O2 in PAAm nanogels, which together enhance the local reaction rate and realize an overall improvement in catalytic efficiency.