Redox Recycling-Triggered Peroxidase-Like Activity Enhancement of Bare Gold Nanoparticles for Ultrasensitive Colorimetric Detection of Rare-Earth Ce 3+ Ion.

Although it has been demonstrated that rare-earth elements (REEs) disturb and alter the catalytic activity of numerous natural enzymes, their effects on nanomaterial-based artificial enzymes (nanozymes) have been seldom explored. In this work, the influence of REEs on the peroxidase-like activity of bare gold nanoparticles (GNPs) is investigated for the first time, and a new type of Ce ³⁺ -activated peroxidase mimetic activity of GNPs is obtained. The introduced Ce ³⁺ can be bound to the bare GNP surface rapidly through electrostatic attraction, after which it donates its electron to the bare GNP. As H ₂ O ₂ is a good electron scavenger, more ^• OH radicals are generated on the surfaces of the bare GNPs, which can considerably enhance TMB oxidation. Due to its redox cycling ability, the activation effect of Ce ³⁺ is proved to be more efficient in comparison to those of the other reported metal ion activators (e.g., Bi ³⁺ , Hg ²⁺ , and Pb ²⁺ ). In addition, it is determined that Ce ³⁺ should directly contact with the gold core to trigger its activation effect. When the surface states of the bare GNPs are altered, the Ce ³⁺ -stimulated effect is strongly inhibited. Furthermore, a novel colorimetric method for Ce ³⁺ is developed, on the basis of its enhancing effect on the peroxidase mimetic activity of bare GNPs. The sensitivity of this newly developed method for Ce ³⁺ is excellent with a limit of detection as low as 2.2 nM. This study not only provides an effective GNP-based peroxidase mimic but also contributes in realizing new applications for nanozymes.