Size Effect in Pd-Ir Core-Shell Nanoparticles as Nanozymes.

Comprehensive study on the size effect in nanozyme (i.e., nanomaterial with enzyme-like activities) based catalysis has rarely been reported. In this work, we systematically investigate the size effect in nanozyme using Pd-Ir core-shell nanoparticles with peroxidase-like activities as a model system. Pd-Ir nanoparticles with four different sizes (3.3, 5.9, 9.8 and 13.0 nm), but identical shapes and surface structures, were designed and synthesized. We found the catalytic activity for individual nanozymes increased with particle size. The area-specific catalytic activity was similar for nanoparticles of 3.3-9.8 nm but was slightly decreased when particle size reached to 13.0 nm. Using enzyme-linked immunosorbent assay (ELISA) as a model platform, size effect of Pd-Ir nanoparticles in biosensing applications was investigated, where smaller nanoparticles were found to offer lower detection limits. This work not only demonstrates the size effect, but also provides an effective strategy to enhance the performance of nanozymes in certain applications.