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

Comprehensive studies on the size effect in nanozyme (i. e., nanomaterials with enzyme-like activities)-based catalysis have rarely been reported. In this work, we systematically investigated the size effect in nanozymes by 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 that 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 decreased slightly when particle size reached 13.0 nm. By using an enzyme-linked immunosorbent assay (ELISA) as a model platform, the size effect of Pd-Ir nanoparticles in biosensing applications was investigated; 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.