Yuan Qin,Huimei Liang,Jia Wu,Zheyang Chi,Shulin Zhao,Fanggui Ye
Natural enzyme cascades, including the same and different kinds of enzymes, have been widely used in biosensing. However, it is still a challenge for nanozymes, the mimics of natural enzymes, to achieve biosensing with different types of enzyme-like activities based on cascade reactions, such as hydrolase and oxidoreductase. Considering the characteristics of the multienzyme-like activity of some nanozymes, as a proof of concept, this study demonstrates a Cu/Ce-MOF-808 nanozyme as a self-cascade catalyst with hydrolase-like and catechol oxidase-like activities. Taking organophosphorus pesticides as an example, we constructed a self-cascade catalytic reaction for the one-step colorimetric detection of isocarbophos. Specifically, the hydrolase-like activity of Cu/Ce-MOF-808 can hydrolyze isocarbophos to produce colorless isopropyl salicylate, which is further oxidized by the catechol oxidase-like activity of Cu/Ce-MOF-808 and complexed with 4-aminoantipyrine (4-AAP) to produce red quinoneimine under neutral conditions with illumination. Thus, a colorimetric strategy for sensitive isocarbophos analysis is developed, with a linear range of 0.90–400.00 μg·mL–1 and a detection limit of 0.42 μg·mL–1. This research presents a new approach to the design and synthesis of nanozymes and has great application potential in the field of nanozyme cascade biosensing.
The dual enzyme-like activities (phosphatase-like activity and laccase-like activity) of one nanozyme (Ce-MOF-808) were employed to develop a nanozyme cascade sensor for the facile and selective detection of profenofos. It was found that the nanozyme Ce-MOF-808 had phosphatase-like activity (V max = 0.31 μM/min and K m = 0.014 mM) and laccase-like activity (V max = 6.27 μM/min and K m = 0.033 mM). In the cascade sensor process, profenofos was first hydrolyzed by Ce-MOF-808. The P O bond was cleaved to produce 4-bromo-2-chlorophenol containing phenol through the phosphatase-like activity of nanozyme. The colorless product was efficiently oxidized because of the laccase-like activity of nanozyme, and then reacted with the color rendering agent 4-aminoantipyrine to produce the red quinone imine. The absorbance peak at 510 nm fitted a linear curve. The limit of detection (LOD) was determined to be 3.33 μg/mL in this method. The quantitative detection of profenofos was conducted on a variety of different real samples. Nanozymes could be stored at 4 ℃ for a long time and the detection method was simple and direct. The nanozyme cascade sensor was convenient and rapid for the detection of pesticides and had promising application prospects in the conventional rapid detection of pesticides in the field.
Juan Chen,Linmeng Wang,Hongyi Gao,Rushuo Li,Zhiyuan Liu,Tao Ban,Shunzheng Zhao,Jichao Yang,Ge Wang
Single-atom catalysts (SACs) catalysts have unique electronic properties and geometric structures, offering maximum atom-utilization efficiency. Noble metal-free SACs anchored within metal–organic frameworks (MOFs) enable precise tuning of electronic structures and significantly enhance catalytic activity beyond conventional porous materials. Herein, we synthesized the synthesis of Cu(I)/Ce-MOF-808-EA by anchoring atomically dispersed Cu(II) species onto the open Ce 6 nodes of the Ce-MOF-808 framework, followed by in situ reduction to Cu(I) via ethanol treatment and thermal activation processes. The atomic dispersion and valence transformation of Cu sites on Ce-MOF-808 were confirmed by X-ray Absorption Spectroscopy (XAS), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and X-ray photoelectron spectroscopy (XPS). The resulting Cu(I)/Ce-MOF-808-EA exhibited outstanding catalytic performance for the hydrogenation of Dicyclopentadiene (DCPD), achieving 100 % conversion, 91.54 % selectivity toward Dihydrodicyclopentadiene (DHDCPD), and 8.45 % selectivity toward Tetrahydrodicyclopentadiene (THDCPD) at 100 °C, 2 MPa. Notably, Cu(I)/Ce-MOF-808-EA outperformed other transition metal catalysts (Co/Ce-MOF-808-EA, Ni/Ce-MOF-808-EA and Zn/Ce-MOF-808-EA). For the first time, Density Functional Theory (DFT) calculations, combined with experimental investigations, revealed a low-energy reaction pathway for DCPD hydrogenation, wherein Cu(I) sites, in cooperation with adjacent oxygen atoms, act as bi-active centers to heterolytically cleave H 2 into proton and hydride species (*H δ+ -H δ- ) for subsequent hydrogenation. This study underscores the potential of MOFs as versatile platforms for engineering single-atom catalysts with enhanced catalytic properties.
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