Polyamidoamine PAMAM G3.5-hematin nanozyme with enhanced peroxidase catalytic activities and biocompatibility for <i>in situ</i> hydrogelation

Abstract Hematin has attracted great attention as an alternative catalyst to horseradish peroxidase (HRP) due to its similar structure to the iron-heme group in the center. However, its catalytic activities at neutral pH have been restricted due to poor solubility, which might be a drawback to its biomedical applications. Therefore, in this study, we modified hematin with polyamidoamine G3.5 to create a novel HRP-mimicking biocatalyst (G3.5-He) with enhanced oxidative catalytic activity under neutral pH conditions, which is ultimately used for catalyzing the hydrogelation of phenol-conjugated gelatin. The chemical structure of G3.5-He was analyzed by UV–vis, 1 H-NMR, and Fourier transform infrared spectroscopy, whereas the size and distribution of nanoparticles were investigated by varying the conjugation degree of hematin by transmission electron microscopy and dynamic light scattering measurements. Meanwhile, the catalytic activities of this biomimetic nanoenzyme were carried out on the catechol and rutin oxidation assay, which showed that the G3.5-He possesses comparable activities and is more resistant against H 2 O 2 than the native HRP enzyme. In addition, the G3.5-He was used as an effective biosensor to quantify the glucose level by catalyzing the reaction of H 2 O 2 with ABTS. Interestingly, under the mild aqueous condition, G3.5-He rapidly catalyzed the crosslinking of gelatin-tyramine polymers to the in situ formation of hydrogel, resulting in the in situ formation of hydrogel with excellent biocompatibility and hemocompatibility. Taken together, we suggest the potential of G3.5-He as a biocatalyst to fabricate injectable hydrogels based on phenol-rich polymers for various biomedical applications.