Using photo-induced p-n junction interface effect of CoMn2O4/β-MnO2 oxidase mimetics for colorimetric determination of hydroquinone in seawater

Tb-based Metal-Organic Framework-Referenced Fluorescence Assay for Distinguishing Hydroquinone from Its Isomers and Subsequent Quantitative Visual Detection of Cu2

Hydroquinone (HQ) and copper ions (Cu2+) are categorized as environmental pollutants that are severely limited in water. Designing a selective assay for discriminating HQ from its two isomers and the convenient determination of Cu2+ is of great importance. Herein, a Tb-based metal-organic framework (Tb-MOF) and HQ are assembled innovatively into a ratiometric fluorescence nanoprobe to selectively distinguish HQ and subsequent quantitative visual detection of Cu2+. The native blue emission of HQ at 338 nm is used as a response signal, while Tb-MOF with green fluorescence offers a reference signal at 545 nm. Notably, neither resorcinol (RC) nor catechol (CC) exhibits obvious emission under the same experimental conditions, which enables discriminating HQ from its isomers. Thus, a ratiometric fluorescence method has been designed for the selective detection of HQ with the fluorescence intensity ratio F338/F545 as the readout. The redox reaction between HQ and Cu2+ induces fluorescence quenching of HQ and no change to that of Tb-MOF, resulting in a noticeable color variation from blue-green to green via the naked eye. Furthermore, sensitive visual detection of Cu2+ is achieved with a low detection limit of 1.67 μM using a smartphone. The satisfactory recoveries and good repeatability of quantitative visualization determined in spiked water samples make this sensing platform suitable for on-site monitoring of environmental samples.

Metal-organic framework composite Mn/Fe-MOF@Pd with peroxidase-like activities for sensitive colorimetric detection of hydroquinone

The construction of highly sensitive detection methods for hydroquinone (HQ) in environment and cosmetics is of great significance for environmental protection and human health. In this work, a novel detection method for HQ was successfully developed by constructing a metal-organic framework mimic enzyme colorimetric sensor (Mn/Fe-MOF@Pd1.0) with excellent peroxidase-like activity, which was synthesized by doping manganese ions into Fe-MOF by introducing bimetallic active centers, thereby improving the peroxidase-like activity of Fe-MOF, and the acid resistance and stability of Mn/Fe-MOF were improved by supporting palladium (Pd NPs). It is proven that Mn/Fe-MOF@Pd1.0 promoted the decomposition of hydrogen peroxide (H2O2) to generate active species, therefore, oxidized chromogenic substrate discoloration. On this basis, the detection of HQ based on the Mn/Fe-MOF@Pd1.0 colorimetric sensor was constructed, in which the limit of detection (LOD) was 0.09 μM in the linear range of 0.3-30 μM. Furthermore, Mn/Fe-MOF@Pd1.0 was successfully used for detecting HQ in hydroquinone whitening cream and actual water samples. The successful synthesis of Mn/Fe-MOF@Pd1.0 may provide new insights for further study of the enzyme-like activity of metal-organic framework composites, and the constructed facile and sensitive sensor system could broaden the application prospects of HQ detection.

Turn-on colorimetric detection of hydroquinone based on Au/CuO nanocomposite nanozyme

CuO nanorods bearing Au nanoparticles (Au/CuO nanocomposites) were prepared by a solution-phase synthesis and exhibited efficient hydroquinone (HQ)-oxidase activity with good specificity. The Au/CuO nanocomposites effectively catalyzed the oxidation of colorless HQ to brown benzoquinone with an absorbance maximum at 376 nm but did not catalyze the conversions of catechol or resorcinol. Kinetic studies indicated that the Au/CuO nanocomposites exhibited a strong affinity for HQ, with a Michaelis-Menten constant of K_m = 0.33 mM. Owing to the high catalytic activity and specificity, a strong color was observed at low concentrations of HQ. Quantitative measurement of HQ was performed via colorimetric analysis, which yielded a detection limit of 3 μM with a linear range of 5-200 μM. This colorimetric sensor was successfully applied to an HQ assay of real water samples with satisfactory results.