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A metal organic framework obtained from cerium(III) and trimesic acid was pyrolyzed to obtain a novel nanostructure referred to as CeO2/C nanowires. The experimental parameters temperature, precursor and gas atmosphere were optimized. The nanowires show good dispersion and a large number of oxygen vacancies, and this leads to excellent peroxidase-like activity. The nanowires are stable at pH values between 2 and 10, and in the 4–80 °C temperature range. The peroxidase-mimicking activity was exploited in a sensitive colorimetric method for determination of H2O2 by using 3,3′,5,5′-tetramethylbenzidine as the chromogenic substrate. The absorbance at 652 nm increases linearly in the 0.5 to 100 μM H2O2 concentration range. If glucose oxidase is added to a solution containing glucose, H2O2 will be enzymatically produced. This was exploited to design a new method for determination of glucose. The optical response is linear in the 1–100 μM glucose concentration range, and the detection limit is 0.69 μM (at S/N = 3). The method was successfully applied to the determination of glucose in serum samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel competitive strategy using oxidase nanozyme for glucose detection was proposed. • The strategy shows high detection efficiency with convenience, rapidness, sensitivity all promised. • The strategy can be applied into human serums with good accuracy. Nanozyme-based sensing strategy for glucose generally involves a two-step H 2 O 2 -bridged cascade reaction. However, this two-step cascade reaction always shows a limited detection efficiency for glucose, which hardly makes simply operation, rapid detection, and sensitivity all promised. Herein, a novel strategy for one-step glucose detection was proposed based on the efficiently competitive relationship between glucose oxidase catalyzed glucose oxidation and oxidase nanozyme catalyzed 3,3′,5,5′-tetramethylbenzidine (TMB) colorimetric oxidation. As a proof of concept, Co-Nx sites on porous carbon (Co-Nx/PC) derived from ZIF-67 was selected as the oxidase nanozyme with O 2 -sensitive nature, which can activate O 2 to produce 1O 2 for TMB colorimetric oxidation. In the presence of glucose, the competitive reaction of glucose oxidase catalyzed glucose oxidation occurs, which will obviously inhibit the Co-Nx/PC catalyzed TMB colorimetric oxidation to construct method for glucose detection. The usage of the same reactant O 2 and the production of suppressive H 2 O 2 cause a dual effect to this inhibition. In addition, the available pH range of Co-Nx/PC overlaps with that of glucose oxidase, promising a one pot reaction. The proposed method with Co-Nx/PC as oxidase nanozyme based on one-step competitive strategy for glucose detection possesses high detection efficiency with convenience (one-pot), rapidness (total reaction time of 10 min) and sensitivity (LOD of 0.31 μM) all promised, which is superior among the methods based on two-step one-pot or two-pot cascade strategy. The strategy can be successfully applied into the blood glucose detection in human serums with satisfactory results. Also, the strategy can be scalable to other oxidase nanozyme like Mn 3 O 4. [ABSTRACT FROM AUTHOR]

Constructing hollow mesoporous nanostructures for dispersing catalytically active sites has attracted growing interest. Here, for the first time, Co 3 O 4 hollow nanocages (Co 3 O 4 HNCs) derived from ZIF-67 were prepared for loading iron nanoparticles (FeNPs), resulting in FeNPs@Co 3 O 4 hollow nanocages (FeNPs@Co 3 O 4 HNCs). FeNPs@Co 3 O 4 HNCs were characterized by SEM, TEM, XRD, XPS and FT-IR. The FeNPs@Co 3 O 4 HNCs composites could catalyze the oxidation of TMB into blue product by H 2 O 2 , showing better peroxidase-like activity than FeNPs and Co 3 O 4 HNCs. Notably, kinetic studies indicated that FeNPs@Co 3 O 4 HNCs behaved an excellent affinity to H 2 O 2 with K m value of 0.019 mM, which was 195 times lower than that of HRP. On this basis, a facile colorimetric biosensing method was established to detect glucose. The linear range was 0.5–30 μM, and the limit of detection was 0.05 μM. The proposed sensor was successfully used to determine glucose in human serum samples. The highly catalytic performance of FeNPs@Co 3 O 4 HNCs is attributed to its porous hollow structure, which is beneficial for dispersion of in situ formed FeNPs and for reducing the agglomeration. Further, the FeNPs@Co 3 O 4 HNCs catalysts with porous character provide an essential way to expose active sites as far as possible to the substrate and increase the catalytic active sites. [ABSTRACT FROM AUTHOR]

A facile and rapid post-synthetic strategy was proposed to prepare a glycine functionalized MIL-53(Fe), namely glycine-MIL-53(Fe), by a simple mixing of water dispersible MIL-53(Fe) and glycine. The FT-IR, SEM, XRD and zeta potential were used to characterize the glycine-MIL-53(Fe). The result showed that glycine post-synthetic modification of MIL-53(Fe) did not change in the morphology and crystal structure of MIL-53(Fe). Interestingly, compared with MIL-53(Fe), the glycine-MIL-53(Fe) exhibits an enhanced peroxidase-like activity, which could catalyze the oxidation of TMB by H 2 O 2 to produce an intensive color reaction. Kinetic analysis indicated that the K m of glycine-MIL-53(Fe) for TMB was one-tenth of that of MIL-53(Fe). The glycine-MIL-53(Fe) as peroxidase mimetic displays better stability under alkaline or acidic conditions than MIL-53(Fe). The good performance of glycine-MIL-53(Fe) over MIL-53(Fe) may be attributed to the increase of affinity between TMB and the glycine-MIL-53(Fe). With these characteristics, a simple and sensitive method was developed for the detection of H 2 O 2 and glucose. The linear detection range for H 2 O 2 is 0.10–10 μM with a detection limit of 49 nM, and glucose could be linearly detected in the range from 0.25 to 10 μM with a detection limit of 0.13 μM. The proposed method was successfully used for glucose detection in human serum samples. [ABSTRACT FROM AUTHOR]

Various analytical applications of metal-organic frameworks (MOFs) have been rapidly developed in the past few years. However, the employment of MOFs as catalysts in chemiluminescence (CL) analysis is rare. Here, for the first time, we found that MIL-53(Fe) MOFs could significantly enhance the CL of luminol in the presence of HO in an alkaline medium. The CL intensity in the luminol-HO-MIL-53(Fe) system was about 20 times higher than that in the luminol-HO system. Moreover, the XRD pattern of MIL-53(Fe) after CL reaction was almost the same as that of the original MIL-53(Fe), confirming the catalytic role of MIL-53(Fe) in the luminol-HO-MIL-53(Fe) system. The possible mechanism behind the enhancing phenomenon was discussed based on the results from the CL spectra, FL probe experiments, and active oxygen species measurements. By coupling with the glucose oxidase-based catalytic oxidation reaction, a sensitive and selective CL method was developed for the detection of glucose. There is a linear relationship between the logarithm of CL intensity and the logarithm of glucose concentration in the range from 0.1 to 10 μM, and a detection limit of 0.05 μM (S/N = 3) is obtained. The proposed method has been applied to the determination of glucose in human serum samples with satisfactory results. [ABSTRACT FROM AUTHOR]