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Exploring highly active nanozymes is an important task to realize the real-time detection of some heavy metal ions in water. In this work, yolk–shell Co3S4 microspheres have been verified to possess excellent peroxidase-like activity, which can be further improved by adding Hg2+. Very interestingly, Hg2+ can trigger "ON" the oxidase-like activity of Co3S4 microspheres. The dual peroxidase-/oxidase-like activity of the yolk–shell Co3S4 microspheres is evaluated by using the chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB). Furthermore, comprehensive studies verify that the enhanced peroxidase-like activity, together with the "ON" oxidase-like activity of the yolk–shell Co3S4 microspheres, is attributed to the in situ generation of HgS on the surface of Co3S4 microspheres and then the release of more active sites. Importantly, the in situ generated HgS on the surface of Co3S4 microspheres can form a heterojunction, which also accelerates the catalytic process. During the catalytic reaction, some active species (O2− and h+) can be detected by ESR. Thus, a colorimetric sensing platform based on Hg2+-triggered signal amplification has been successfully constructed, which can be validated by the detection of Hg2+ residue in environmental water. [ABSTRACT FROM AUTHOR]

The peroxidase-like activity of CdV2O6 nanorods has been considerably improved by modification with N, N-dicarboxymethyl perylene-diimide (PDI) as a photosensitizer. The peroxidase-like behaviors are evaluated by virtue of the colorless chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB), which is fast changed into blue oxTMB in the presence of H2O2 in only 90 s. PDI-CdV2O6 exhibits high stability at elevated temperatures and PDI-CdV2O6 retains more than 70% of its catalytic activity over a wide range of 15 to 60 °C. The catalytic mechanism of PDI-CdV2O6 is ascribed to the synergistic interaction between PDI and CdV2O6 and the generation of •O2− radicals. Based on the enhanced peroxidase-like activity of PDI-CdV2O6, a selective colorimetric sensor has been constructed for H2O2 and pyrogallol (PG) with detection limits of 36.5 μM and 0.179 μM, respectively. The feasibility of the proposed sensing platform has been validated by detecting H2O2 in milk and pyrogallol in tap water. [ABSTRACT FROM AUTHOR]

Nanomaterials with peroxidase-like activity have shown potential for hydrogen peroxide (H2O2) detection. However, the difficult separation and poor reusability of nanoparticles have hindered their further applications. Herein, we report a novel reusable peroxidase mimic, Co/Fe/NiOx@NF, prepared by in situ self-assembly of 3D hierarchical Co–Fe–Ni mixed oxides on nickel foam. The Co/Fe/NiOx@NF exhibited peroxidase-like activity, and we constructed a simple and convenient colorimetric sensing platform for H2O2 detection. The sensing platform displayed good linearity with a H2O2 concentration ranging from 0.2 to 4 mM and a low detection limit of 32.9 μM. We also applied the platform for the detection of H2O2 in actual samples and obtained satisfactory results. Due to the ferromagnetic properties and macro three-dimensional size of nickel foam, Co/Fe/NiOx@NF can be easily recycled using a magnet or tweezers, eliminating the need for high-speed centrifugation as in typical nanozyme systems. Furthermore, the catalytic activity of Co/Fe/NiOx@NF remained stable after one hundred successive cycles, demonstrating its potential for reuse. This feature reduces waste and cost and makes it an environmentally friendly and efficient method for H2O2 detection. [ABSTRACT FROM AUTHOR]

Development of efficient non-precious and abundant electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the key tasks in renewable energy technologies. Transition-metal selenides have been widely studied as promising candidates. Herein, a layer-structured CoSe2 was used as a precursor, followed by simple one-step dopamine coating. The as-prepared Co0.85Se@NC showed outstanding performance in both ORR and OER catalysis. The onset potential and half-wave potential of the ORR in 0.1 M KOH solution can reach 0.96 V and 0.85 V, respectively. The OER overpotential corresponding to 10 mA cm−2 in 1.0 M KOH solution is only 350 mV, which is much smaller than that of RuO2 (390 mV). Importantly, the catalyst showed good stability, demonstrating that the layered Co0.85Se@NC has great potential for advanced bifunctional electrocatalysis. [ABSTRACT FROM AUTHOR]

Exploring highly active peroxidase mimics at physiological pH is important for the construction of efficient and convenient colorimetric sensing platforms for detecting small biomolecules. In this work, prepared zinc pyrovanadate (Zn3V2O7(OH)2·2H2O) nanorods exhibit excellent peroxidase-like activity, which is verified by the fast oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) into a blue product (oxTMB) by H2O2 at physiological pH (pH = 7) in 2 min. In addition, the catalytic behaviors of Zn3V2O7(OH)2·2H2O as a peroxidase-like nanozyme conform to the Michaelis–Menten equation. Scavenger experiments prove that the catalytic activity of Zn3V2O7(OH)2·2H2O is ascribed to ˙O2− radicals generated in the process of catalysis. Based on the peroxidase-like activity of the Zn3V2O7(OH)2·2H2O nanozyme, a fast and convenient colorimetric sensor has been constructed to detect H2O2 and epinephrine (EP) under physiological pH. The detection limit of EP is as low as 0.26 μM. In addition, the feasibility of the proposed sensor has been validated to detect H2O2 in milk and EP in serum. [ABSTRACT FROM AUTHOR]

Some nanoperoxidase-based colorimetric sensors have been used to detect only one molecule at a time. Thus, the simultaneous detection of various molecules coexisting in the same system is a great challenge. In this work, an excellent nanoperoxidase, nickel cobalt Prussian blue analogue-MoS2 nanoboxes (PBA-MoS2), have been successfully prepared by the hydrothermal method and used to construct a colorimetric sensing array to determine a series of reductive substances containing the catechol structure (such as catechol, epinephrine hydrochloride, procyanidin, caffeic acid and dopamine hydrochloride). The excellent peroxidase-like activity of PBA-MoS2 is verified by the chromogenic reaction of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2 in 2 min. The catalytic mechanism of PBA-MoS2 is attributed to generated reactive species including holes (h+) and superoxide radicals (˙O2−) in the process of catalysis. The fast economic H2O2 colorimetric sensing array has been constructed based on the PBA-MoS2 nanoperoxidase. Due to the presence of different reducing substances, the catalytic oxidation of TMB can be restricted to different extents, accompanied by blue colour changes to varying degrees. Therefore, on combining PBA-MoS2 nanoperoxidase with H2O2 and TMB, five reductive substances can be quantitatively distinguished by linear discriminant analysis (LDA) at the 2 mM level. [ABSTRACT FROM AUTHOR]

An ultrasensitive electrochemiluminescence (ECL) biosensor was developed based on MIL-53(Al)@CdS QDs and SiO2@AuNPs for trichlorfon detection. Metal–organic frameworks (MOFs) were used as a loading platform that provided a large surface area to load targets and modified materials onto the electrode. At the same time, SiO2@AuNPs loaded plenty of AuNPs which effectively increased the ECL resonance energy transfer between the CdS QDs, so that the ECL signal was strongly quenched and resulted in an amplified response. In the range of 10−11–10−4 M, the ECL response showed a linear relationship with the concentration (logarithm) of trichlorfon, and the detection limit was 5.1 × 10−12 M (S/N = 3). When the biosensor was applied to detect trichlorfon in lettuce, broccoli, cucumber, and chives, the recoveries obtained from the spiked samples were 97%–105%, 102%–104%, 100%–104%, and 98%–104%, respectively. Thus, this novel ECL biosensor has potential applications for the analysis of trichlorfon in food samples. [ABSTRACT FROM AUTHOR]

5,10,15,20-Tetrakis(4-carboxyl phenyl)porphyrin (Por) modified Co(OH)2 deposited on the surface of GO nanocomposites (Por/Co(OH)2/GO) were prepared and characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and XRD. For the first time, H2TCPP/Co(OH)2/GO is found to have enhanced peroxidase-like activity and catalyze the oxidation of the substrate 3,3,5,5-tetramethylbenzidine (TMB) by hydrogen peroxide (H2O2). Notably, the colorless TMB rapidly transformed into blue oxTMB in just 60 s, which was easily observed visually. The catalytic kinetics of H2TCPP/Co(OH)2/GO is in accord with the Michaelis–Menten equation. The catalytic mechanism of H2TCPP/Co(OH)2/GO nanocomposites is attributed to hydroxyl radicals (˙OH), due to decomposition of H2O2, which is verified by using terephthalic acid as a fluorescent probe. What's more, H2O2 can be detected in a wide linear detection range from 5 to 35 mM with a detection limit of 0.385 mM. Furthermore, based on the excellent peroxidase-like activity of H2TCPP/Co(OH)2/GO, a colorimetric sensor is established to sensitively detect glutathione (GSH) in a linear range from 10 to 300 μM with a low detection limit of 9.5 μM. [ABSTRACT FROM AUTHOR]