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Four kinds of Ag3PO4 materials were prepared by controlling the experimental conditions, which were developed as oxidase mimics. Experimental results showed that different synthesis methods led to distinct crystal structures, morphologies, and surface properties, which contributed to diverse oxidase-like activities of Ag3PO4 materials. Among them, Ag3PO4 microcubes (APMCs) can efficiently catalyze the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine in the presence of dissolved oxygen to form a blue-colored oxide, presenting the best intrinsic oxidase mimetic ability. The higher-energy [110] facets with more oxygen vacancies exposed and more active sites coupled with more negative charge and larger specific surface area of APMCs contributed to its enhanced oxidase mimetic performance. Besides, mercury ions were proved to remarkably and selectively stimulate the oxidase-like ability of APMCs owing to the formation of Ag–Hg amalgam on its surface. Based on the stimulating effect of Hg2+ towards APMCs, a simple and rapid method for colorimetric determination of Hg2+ was thus established via the significant signal amplification and megascopic color variation. Under the optimal conditions, the sensing system showed a good linear relationship ranging from 0.1 to 7.0 μM and a detection limit of 20 nM for Hg2+, exhibiting high selectivity and good colour stability. Moreover, the colorimetric method was successfully applied to determine Hg2+ in real water samples. Considering these advantages, the developed colorimetric sensing system is expected to hold bright prospects for trace determination of Hg2+ in biological, environmental, and food samples. [ABSTRACT FROM AUTHOR]

CoMoO4 materials were prepared through a simple hydrothermal method and developed as highly efficient peroxidase mimics for colorimetric determination of H2O2. Based on the different experimental conditions in the synthesis process, the CoMoO4 materials present distinct morphologies, structures, surface properties, and peroxidase mimetic activities. Among them, CoMoO4 nanobelts (NBs) display the best intrinsic peroxidase mimetic abilities due to the high-energy (100) facet exposed, more Co active sites at (100) facet, more negative potential, and larger specific surface area. It can efficiently catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 to generate a blue oxide. In view of the excellent peroxidase mimetic catalytic activity of CoMoO4 NBs, a rapid, convenient, and ultrasensitive method was successfully established for the visual and colorimetric determination of H2O2. The method exhibits good selectivity, practicability, stability, and reusability, and has a detection limit of 0.27 μM. The peroxidase mimetic catalytic mechanism of CoMoO4 NBs was illustrated according to the kinetic and active species trapping experiments. The method has a good potential for rapid and sensitive determination of H2O2 for biomedical analysis. [ABSTRACT FROM AUTHOR]

In this study, yttrium vanadate (YVO 4) flower-like microstructures assembled by quadrangular prisms (YVFPs) were prepared through a facile hydrothermal method, which were developed as a novel nanoenzyme to determine hydrogen peroxide (H 2 O 2) for the first time. In the presence of H 2 O 2 , YVFPs exhibited a highly efficient peroxidase-like activity in catalyzing the oxidation the typical peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB). Colorless TMB would be turned into oxidized TMB with a visible blue color and UV–visible absorption peak at 652 nm. The catalytic reaction mechanism was proposed according to the kinetics experiments and active species capture tests, indicating that·O 2 - radicals played a key role in the peroxidase mimetic reaction. Besides, YVFPs showed a superior affinity to TMB compared with the natural enzyme horse radish peroxidase with a lower K m value. Taking advantage of the strong peroxidase-like activity of YVFPs, a simple, rapid, sensitive, and visual platform was successfully established for colorimetric detection of H 2 O 2. The YVFPs-based colorimetric system possessed good selectivity, stability and reusability with a wider linear range from 0.5 μM to 50 μM and a lower detection limit as low as 0.126 μM towards H 2 O 2 determination. Moreover, the feasibility of this convenient method was further validated by assaying residual H 2 O 2 in milk and contact lens solutions. This work not only provides a novel artificial biomimetic catalyst with efficient catalytic abilities, but also opens up a new potential application field of YVO 4 materials in clinical diagnosis, food safety and biomedicine. [Display omitted] • YVO 4 flower-like microstructures assembled by quadrangular prisms were successfully prepared. • YVO 4 was developed as a novel nanoenzyme for colorimetric detection of H 2 O 2 for the first time. • YVO 4 possessed a highly efficient peroxidase-like catalytic activity. • A rapid and ultrasensitive method was established for assaying H 2 O 2 based on YVO 4 with a detection limit as low as 0.126 μM. • The YVO 4 -based assay system revealed a high selectivity, stability, reusability, and practicability in H 2 O 2 detection. [ABSTRACT FROM AUTHOR]

• Ag@Ag 2 WO 4 NRs was firstly applied as oxidase mimics with highly efficient oxidase-like activities. • Ag@Ag 2 WO 4 NRs can efficiently catalyze the chromogenic reaction of TMB based on the stimulating effect of Hg2+. • The introduction of Ag NPs on the surface of Ag 2 WO 4 NRs highly enhanced the oxidase-like abilities. • A rapid and ultrasensitive colorimetric method was established for assaying Hg2+. • The colorimetric sensing approach revealed a high selectivity, good stability and favorable actual applicability. In this paper, four kinds of Ag 2 WO 4 materials were synthesized via facile hydrothermal methods, which were developed as highly efficient biomimetic catalysts for the first time. These Ag 2 WO 4 materials exhibited distinct oxidase-like activities owing to their different crystal structures, morphologies and surface properties. Among them, Ag@Ag 2 WO 4 nanorods (AWNRs-9) exhibited the best intrinsic oxidase mimetic performance, which were composed of Ag nanoparticles (NPs) loading on the surface of Ag 2 WO 4 nanorods (NRs). It is found that the introduction of Ag NPs can significantly enhanced the oxidase-like catalytic activity due to the synergistic effect between Ag NPs and Ag 2 WO 4 NRs. In addition, the catalytic oxidation reaction of 3,3′,5,5′-tetramethylbenzidine by AWNRs-9 was dramatically and selectively enhanced due to the mercury-stimulated effect. Thus, a simple, rapid and sensitive method for colorimetric detection of Hg2+ was developed, displaying a good linear response in the range of 0.25 μM to 8.0 μM with a detection limit of 1.6 nM. This assay method also showed a high selectivity, good stability and favorable practicability. It was successfully applied to the detection of Hg2+ in real water samples. This sensing system is expected to hold bright prospects for quantitative detection of Hg2+ in biological, environmental, and food fields. [ABSTRACT FROM AUTHOR]

In this paper, nanoparticles decorated Ce 2 (WO 4) 3 nanosheets (CWNSs) with negative potential and large specific surface area were synthesized and developed as highly efficient peroxidase mimics for colorimetric detection of H 2 O 2. CWNSs can efficiently catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H 2 O 2 to induce an obvious color variation. Kinetic analysis indicated that the catalytic behaviors of CWNSs obey the typical Michaelis-Menten mechanism. The peroxidase-like catalytic mechanism of CWNSs was proposed according to the active species trapping experiments, verifying that ·O 2 – radicals played primary roles in the catalytic reaction. Based on the strong and stable peroxidase-like catalytic activity of CWNSs, a simple, rapid, selective, and ultrasensitive method was successfully established for colorimetric detection of H 2 O 2. The method has a good linear response ranging from 0.5 μM to 100 μM for H 2 O 2 concentration with a lower detection limit of 0.15 μM. Benefitting from the sensitive response and good stability, the method is applied in real sample detection and shows a favorable reproducibility and feasibility. This work not only provides a novel enzymatic mimics with remarkable catalytic activities for biomedical and environmental analysis, but also extends the application area of Ce 2 (WO 4) 3 materials. Unlabelled Image • Ce 2 (WO 4) 3 nanosheets were developed as highly efficient peroxidase mimics for colorimetric detection of H 2 O 2 firstly. • CWNSs possessed a nice peroxidase-like activity owing to the negative potential and large specific surface area. • CWNSs exhibited a stronger binding affinity with TMB compared to HRP. • A rapid and ultrasensitive method was established for detecting H 2 O 2 based on CWNSs with a detection limit of 0.15 μM. • The sensing system revealed a high selectivity, stability and reusability. [ABSTRACT FROM AUTHOR]

CoMoO4 materials were prepared through a simple hydrothermal method and developed as highly efficient peroxidase mimics for colorimetric determination of H2O2. Based on the different experimental conditions in the synthesis process, the CoMoO4 materials present distinct morphologies, structures, surface properties, and peroxidase mimetic activities. Among them, CoMoO4 nanobelts (NBs) display the best intrinsic peroxidase mimetic abilities due to the high-energy (100) facet exposed, more Co active sites at (100) facet, more negative potential, and larger specific surface area. It can efficiently catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 to generate a blue oxide. In view of the excellent peroxidase mimetic catalytic activity of CoMoO4 NBs, a rapid, convenient, and ultrasensitive method was successfully established for the visual and colorimetric determination of H2O2. The method exhibits good selectivity, practicability, stability, and reusability, and has a detection limit of 0.27 μM. The peroxidase mimetic catalytic mechanism of CoMoO4 NBs was illustrated according to the kinetic and active species trapping experiments. The method has a good potential for rapid and sensitive determination of H2O2 for biomedical analysis. [ABSTRACT FROM AUTHOR]