Abstract
Metal–organic framework (MOF) nanozymes, as emerging members of the nanozymes, have received more and more attention due to their composition and structural characteristics. In this work, we report that mixed-valence state Ce-MOF (MVCM) has intrinsic haloperoxidase-mimicking activity. MVCM was synthesized by partial oxidation method using Ce-MOF as a precursor. In the presence of H2O2 and Br−, MVCM can catalyze oxidative bromination of chromogenic substrate phenol red (PR) to produce the blue product bromophenol blue (Br4PR), showing good haloperoxidase-like activity. Because of the special chromogenic substrate, we constructed a ratiometric colorimetric-sensing platform by detecting the absorbance of the MVCM-(PR, Br−) system at wavelengths of 590 and 430, for quantifying H2O2, where the detection limit of the H2O2 is 3.25 μM. In addition, the haloperoxidase-mimicking mechanism of the MVCM is proposed. Moreover, through enzyme kinetics monitoring, the Km (H2O2 and NH4Br) of the MVCM is lower than that of cerium oxide nanomaterials, indicating that the MVCM has a stronger binding affinity for H2O2 and NH4Br than other materials. This work provides more application prospects for the development of nanozymes in the field of biosensors in the future.
Highlights
Nanozymes, as a new type of natural enzyme mimics, have been intensively studied for decades [1]
The results showed that the crystal structure of mixed-valence state Ce-metal–organic frameworks (MOFs) (MVCM) remained after partial oxidation treatment
MVCM presented the functional groups similar to that of Ce-MOF according to the FT-IR spectrum (Figure 2B)
Summary
As a new type of natural enzyme mimics, have been intensively studied for decades [1]. Applications based on nanozyme sensing mainly contain electrochemical sensing [3], chemiluminescence sensing [4], surface-enhanced Raman scattering (SERS) sensing [5], fluorescence sensing [6], and colorimetric sensing [7] Among these biosensor methods, sensing methods based on fluorescence and colorimetry have received extensive attention because of their convenience, cheapness, and high sensitivity [8]. Due to the bathochromic shift of the absorption peak caused by the oxidative bromination of phenol red to bromophenol blue, a ratiometric colorimetric sensor for detecting H2O2 was designed (Figure 1). The present work brings new insight into colorimetric sensors and provides a novel, low-cost method for the visual detection of H2O2, which makes MVCM have a broad application prospect in biomedical analysis and other related fields. The reaction conditions (pH, temperature, incubation time, the concentrations of MVCM, PR and NH4Br) and the bromine source were studied
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