Although it has been demonstrated that rareearth elements (REEs) disturb and alter the catalytic activity of numerous natural enzymes, their effects on nanomaterialbased 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.
In this study, on the basis of the biomineralization capability of urease, a facile, one-step, and green synthetic method has been proposed for the fabrication of gold nanoclusters (AuNCs). The prepared urease-encapsulated AuNCs (U-AuNCs) exhibited strong red fluorescence emission (λ em = 630 nm) with a quantum yield as high as 17%. Interestingly, at a low concentration, the U-AuNC solution was found to be a dual-emissive system with the blue emission of the dityrosine (diTyr) residues of urease and the red emission of the embedded AuNCs. Further experiments demonstrated that p-nitrophenol (PNP) can selectively suppress the 410 nm emission of the diTyr residues of U-AuNCs without affecting the red emission of the U-AuNCs. The fluorescence quenching mechanism between U-AuNCs and PNP was systematically studied, and the leading role of the inner filter effect (IFE) was identified. Additionally, based on the sulfatase-catalyzed hydrolysis of p-nitrophenyl sulfate (PNPS) to release PNP, a self-referenced ratiometric detection method for sulfatase, which plays a crucial role in sulfur cycling, degradation of sulfated glycosaminoglycans and glycolipids, and extracellular remodeling of sulfated glycosaminoglycans, was developed by using dual-emissive U-AuNCs as the signal readout, in which the diTyr residues served as the probe and the AuNCs functioned as the internal reference. This IFEbased ratiometric sensing strategy showed a good linear relationship over the range of 0.01−1 U/mL (R 2 = 0.997). The detection limit for sulfatase activity was 0.01 U/mL. The developed protocol was successfully used to detect sulfatase activity in human serum samples. The simplicity, rapidity, low cost, high credibility, good reproducibility, and excellent selectivity of the detection platform serve as an inspiration for further applications of fluorescent AuNCs in chemo/biosensing.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.