Enhancing Fenton-like Biocatalysis of CuPd Bimetallic Nanozymes by Alkylamine Ligand Self-Assembled Monolayers

Abstract

The synergistic effect of copper and palladium makes CuPd bimetallic nanozymes potential candidate for tumor biocatalysis. However, the practical catalytic activity is closely related to their surface modification and structure. In thzis study, CuPd nanozymes were prepared by one-step reduction method using various surface ligands (decamethylamine (DA), dodecamethylamine (DDA), hexadecamethylamine (HDA), and octadecamethylamine (ODA)) with different alkylamine length in order to study the effects of surface self-assembled monolayers (SAMs) formed by ligands. TEM, XPS, and XRD results showed that all four nanozymes were similar for their structures, sizes, and compositions. However, as-synthesized CuPd@DA and CuPd@HDA presented higher Fenton-like activity due to the lower steric hindrance brought by ordered and thinner SAMs. In contrast, both CuPd@DDA and CuPd@ODA exhibited weak biocatalytic activity for the thicker and stacked SAMs because of the long length of alkylamine ligands. In vitro anti-tumor cytotoxicity showed the lower IC50 value of CuPd@DA (104.6 μg/mL) and CuPd@HDA (118.6 μg/mL), and the higher value for CuPd@DA and CuPd@HDA, demonstrating the biocatalytic differences caused by surface SAMs. This study provides unique insights for optimizing biocatalytic effect of bimetallic nanozymes in the perspective of surface SAMs.