Redox Recycling-Triggered Peroxidase-Like Activity Enhancement of Bare Gold Nanoparticles for Ultrasensitive Colorimetric Detection of Rare-Earth Ce 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-activated peroxidase mimetic activity of GNPs is obtained. The introduced Ce can be bound to the bare GNP surface rapidly through electrostatic attraction, after which it donates its electron to the bare GNP. As HO 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 is proved to be more efficient in comparison to those of the other reported metal ion activators (e.g., Bi, Hg, and Pb). In addition, it is determined that Ce should directly contact with the gold core to trigger its activation effect. When the surface states of the bare GNPs are altered, the Ce-stimulated effect is strongly inhibited. Furthermore, a novel colorimetric method for Ce 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 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.