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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]

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]

Encapsulating metal nanoparticles (NPs) into carbon materials is a promising strategy for the fabrication of nanozymes with high activity. Here, for the first time, the proof-of-concept is demonstrated by fabricating CoNPs embedded in NH 2 -MIL-88(Fe) MOFs-derived magnetic carbon (MC) through in situ reduction of cobalt precursors by NaBH 4 . The obtained CoNPs/MC was characterized by TEM, SEM, XPS, XRD, Raman spectrum, and FT-IR. The CoNPs/MC exhibits much higher peroxidase-like activity than pure CoNPs and magnetic carbon. The high peroxidase-like activity of the CoNPs/MC is attributed to the decomposition of H 2 O 2 to generate OH and O 2 − radicals, resulting in TMB color reaction. Also, CoNPs/MC is robust in a wide range of pH and temperature, indicating a promising peroxidase-like candidate. On this basis, a colorimetric assay was developed by combining glucose oxidase with CoNPs/MC for glucose biosensing. The linear range for glucose detection is from 0.25 to 30 μM with a lower detection limit of 156 nM. The CoNPs/MC-based colorimetric method has been successfully used to assay the content of glucose in real biological samples such as human serums. Our work reveals the high potential of encapsulating metal NPs into carbon materials for the fabrication of nanozymes with stable and high activity. [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]

Fe-MIM/ZIF-8 with rich biomimetic iron-imidazole groups was prepared and investigated as superior peroxidase mimic for colorimetric analysis of H 2 O 2 and glucose. [Display omitted] • Biomimetic Fe-MIM/ZIF-8 nanoflower was fabricated and firstly explored as nanozyme. • Fe-MIM/ZIF-8 with rich biomimetic Fe-MIM exhibits superior peroxidase-like activity. • Fe-MIM/ZIF-8 owns a strong affinity for H 2 O 2 with a low K m of 0.028 mM. • The colorimetric biosensor for H 2 O 2 and glucose promises high sensitivity. • The biosensor can detect glucose content in biological samples with high accuracy. The active site of natural horseradish peroxidase (HRP) comprises iron coordinated equatorially by a porphyrin ring and axially by the imidazole group of His170. The low water solubility of porphyrin rings inspired us to investigate the potential of the iron-imidazole group as peroxidase mimic. Herein, iron-imidazole (Fe-MIM) was one-pot constructed using ascorbic acid stabilized Fe2+ and 2-methylimidazole in the presence of zinc acetate at room temperature in aqueous medium, along with the formation of ZIF-8 framework around Fe-MIM sites. Fe-MIM/ZIF-8 was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller surface measurements. Fe-MIM/ZIF-8 exhibits high peroxidase-like activity, efficiently catalyzing the redox reaction between H 2 O 2 and 3, 3′, 5, 5′-tetramethylbenzidine, as made evident by the appearance of a UV–Vis signal at 652 nm. Fe-MIM/ZIF-8 displays higher catalytic activity than the material (Fe + MIM) prepared by ascorbic acid stabilized Fe2+ and MIM, due to its rich biomimetic architecture and large BET surface area. The K m of Fe-MIM/ZIF-8 for H 2 O 2 was 28 μM, which is 132 and 98 times lower than those of HRP and hemin (ironIII porphyrin), respectively. This low K m value indicates the strong affinity of Fe-MIM/ZIF-8 for H 2 O 2 , which proves the superiority of biomimetic Fe-MIM sites and suggests Fe-MIM/ZIF-8′s potential for H 2 O 2 -related biosensing. The highly sensitive colorimetric methods for H 2 O 2 and H 2 O 2 -related glucose detection has been proposed. The applicability of this method to glucose detection in serum samples was tested with satisfactory results. [ABSTRACT FROM AUTHOR]

MoS 2 -MIL-101(Fe) was prepared and investigated for colorimetric analysis of H 2 O 2 and glucose with high selectivity based on a superior peroxidase-like activity. • MoS 2 -MIL-101(Fe) was developed and explored as nanozyme for the first time. • Synergistic interaction in MoS 2 -MIL-101(Fe) leads to superior catalytic activity. • Strong affinity of MoS 2 -MIL-101(Fe) for H 2 O 2 due to the low K m of 0.008 mM. • MoS 2 -MIL-101(Fe) could be used for highly sensitive H 2 O 2 and glucose detection. A novel nanostructure MoS 2 nanoflowers anchoring iron(III)-based metal-organic framework MIL-101(Fe) [Fe 3 O(H 2 O) 2 Cl(O 2 C–C 6 H 4 −CO 2) 3 ], named MoS 2 -MIL-101(Fe), was prepared by growing MIL-101(Fe) crystals with as-prepared MoS 2. Then, MoS 2 -MIL-101(Fe) was characterized through SEM, TEM, BET, XRD, DLS, and XPS. MoS 2 -MIL-101(Fe) possesses synergetic peroxidase-mimicking activity over individual MIL-101(Fe) and MoS 2 , which can catalyze the oxidation of TMB by H 2 O 2 with a much stronger Vis-absorption. MIL-101(Fe) has a high porosity and large specific surface area for MoS 2 to absorb H 2 O 2 and TMB. Hydrophilic MIL-101(Fe) could prevent the aggregation of hydrophobic MoS 2 in aqueous solution, which is beneficial for catalysis. In addition, anchored MoS 2 brings mesopore and abundant exposed active units to the MIL-101(Fe) surface. The synergetic effects result in a highly enhanced catalytic performance. The Michaelis constant (0.008 mmol/L) of MoS 2 -MIL-101(Fe) for H 2 O 2 is 462 times lower than that of HRP, showing its strong affinity with H 2 O 2. On the basis, a sensitive method for H 2 O 2 detection was proposed with a linear range of 0.01−20 μmol/L and a detection limit of 10 nmol/L. Considering H 2 O 2 as product in the reaction of glucose catalyzed by glucose oxidase, a sensitive and selective method for glucose detection was proposed. The method can be used in blood glucose detection with good accuracy. [ABSTRACT FROM AUTHOR]