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The multifunctional hemin@carbon dot hybrid nanozymes (hemin@CD) with simultaneous peroxidase-like activity and fluorescence signalling property was prepared for the first time. Based on these properties, hemin@CD was applied to develop a dual-channel fluorescent probe for H2O2 and H2O2-based biocatalytic systems. By virtue of the peroxidase-like activity, hemin@CD can catalyze the oxidative coupling of 4-aminoantipyrine with phenol in the presence of H2O2 to form a pink-red quinoneimine dye with a maximum absorbance at 505 nm. Under the excitation wavelength of 480 nm, the green fluorescence of hemin@CD peaks at 540 nm and is quenched by the generated quinoneimine dye due to an inner filter effect, and also by H2O2 because of dynamic quenching. Thus, a colorimetric and fluorimetric dual-channel optical probe for H2O2 is obtained. Due to the glucose/xanthine transformations under formation of H2O2 by the relevant oxidase catalysis, the probe can be applied for detection of glucose and xanthine. The colorimetric detection limits for H2O2, glucose and xanthine are 0.11, 0.15, 0.11 μM, and the and fluorimetric detection limits are 0.15, 0.15, 0.12 μM, respectively. [ABSTRACT FROM AUTHOR]

Abstract Nanozymes' activities could be regulated by a simple and effective pH change in an in situ manner. In this work, for the first time, the peroxidase-like activity of Ni/Co layered double hydroxides (LDHs) was regulated via the alkaline-promoted reaction of fluorogenic substrate homovanillic acid and H 2 O 2 , and a promising tool for pH sensing was developed over the pH range of 8.3–9.6. As peroxidase nanozyme model, Ni/Co LDHs showed ease of preparation, low-cost, and water-solubility, which played an important role in this luminescence system. Based on the pH-dependent regulation of the Ni/Co LDHs activity, we constructed the bioassay platform for the determination urea, urease, penicillin G, and penicillinase with a wide linear range of 17–1000 µM, 3.3–270 mU mL−1, 3.3–1300 µM and 3.3–100 mU mL−1, respectively. This study not only demonstrated the alkaline-promoted modulation the nanozymes' activities, but also established a facile approach to develop novel bioassays. Graphical abstract fx1 Highlights • The alkaline-promoted regulating Ni/Co LDHs' peroxidase-like activity has been explored. • A pH sensor was developed based on the system of Ni/Co LDHs-HVA-H 2 O 2. • A platform for the detection urea, urease, penicillin G, and penicillinase was established. [ABSTRACT FROM AUTHOR]

Nanomaterial-based peroxidase-mimetics are an emerging research field that promises to produce alternatives to horseradish peroxidase for a variety of applications. Generally, some peroxidase-mimetics substrates are used in acidic condition (pH ≤ 7). Then, it is necessary to screen some peroxidase-mimetics substrates suitable for basic condition because that some peroxidase-mimetics leached ions in acidic solution. In this paper, using Ni/Co layered double hydroxides (LDHs) as a nano-peroxidase mimic model, we evaluated three fluorogenic substrates suitable for basic condition though experimental conditions, reaction kinetic and glucose detection assay. And the detection of glucose method based on homovanillic acid (HVA) as fluorescent substrate gave wide linear range (0.02–20 μM) and low detection limit (0.01 μM). We also developed a novel platform that could study the inhibitory effects of ascorbic acid and glutathione based on the system of Ni/Co LDHs-HVA-H 2 O 2 . [ABSTRACT FROM AUTHOR]

The synthesized NiCo 2 O 4 mesoporous spheres (MS) displayed intrinsic peroxidase and oxidase-like activity were firstly reported. The catalytic mechanism of the oxidase-like activity of NiCo 2 O 4 MS was analyzed in detail using the electron spin resonance (ESR) method. It is found that NiCo 2 O 4 MS could directly oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) but did not produce 1 O 2 and ·OH. And the mechanism of the peroxidase-like activity of NiCo 2 O 4 MS was also verified that the oxidation of TMB stemmed from not only ·OH but also 1 O 2 . Based on the NiCo 2 O 4 MS showed excellent peroxidase-like activity over a broad temperature range, especially at normal body temperature, a detection tool was designed for glucose determination in diabetics' serum samples. And this detection method based on NiCo 2 O 4 MS gave a lower limit of detection than the method using Co 3 O 4 NPs and NiO NPs, as the single-component oxides of NiCo 2 O 4 . Our study may open up the possibility to make a great influence on the next generation of enzyme mimetics system. [ABSTRACT FROM AUTHOR]

Ultra-thin MoS 2 nanosheets were treated by nitrogen (N 2) plasma to mediate the photo-reduction deposition of silver forming N/Ag@MoS 2 nanozymes for the catalysis-based colorimetric assay of hydrogen sulfide (H 2 S) in aquaculture water. [Display omitted] • MoS 2 nanosheets were treated by N 2 plasma to mediate the robust deposition of silver. • Enhanced electron transferring of N/Ag@MoS 2 can be achieved. • The deposited silver can act as a specific probe to recognize H 2 S. • N/Ag@MoS 2 can present the enhanced catalysis for the colorimetric analysis of H 2 S. • N 2 plasma treatment route promises the design of various nanozymes with 2D structures. Ultra-thin MoS 2 nanosheets were treated by nitrogen (N 2) plasma to mediate the photo-reduction deposition of silver forming N/Ag@MoS 2 nanozymes for the catalysis-based colorimetric assay of hydrogen sulfide (H 2 S) in aquaculture water. It was found that the as-produced N/Ag@MoS 2 could display a greatly enhanced peroxidase-like catalytic activity than that of MoS 2 nanosheets (about three times higher). Also, in the presence of H 2 S, a strong Ag-S interaction could occur to form non-conductive Ag 2 S onto N/Ag@MoS 2 nanocomposites towards the rationally reduced catalysis depending on H 2 S concentrations. Herein, on the one hand, the plasma treatment-aided doping of N elements into MoS 2 nanosheets might facilitate the robust deposition of silver onto MoS 2 nanosheets through the strong Ag-N chelation, and the enhanced internal electron transferring of N/Ag@MoS 2 nanozymes. On the other hand, the so deposited silver could not only enhance the catalytic properties of nanozymes, but also act as a specific probe for recognizing H 2 S to trigger the decreased catalysis of nanozymes. Importantly, such a N 2 plasma treatment pathway that mediates the deposition of silver onto two-dimensional structures like MoS 2 nanosheets may pave the way toward the design of various nanozymes for the analysis of different targets in the biomedical, food, and environmental monitoring fields. [ABSTRACT FROM AUTHOR]

A nanozyme with 2D/1D heterostructure has been fabricated by the in-situ growth of molybdenum disulfide nanosheets (MoS 2 NSs) onto single-walled carbon nanotubes (SWCNTs). It was discovered that the so-obtained SWCNTs@MoS 2 nanozyme could exhibit greatly improved peroxidase-like catalysis, due to that the formed 2D/1D interfacial coupling in the heterostructure might provide more active sites and exhibit enhanced charge transferring during the catalytic reactions, as confirmed by the X-ray photoelectron spectroscopy, photoluminescence, electrochemical impedance spectra and radical capturing experiments. Furthermore, the catalysis of the developed nanozyme could be selectively inhibited by glutathione (GSH) through the competitive consumption of hydroxyl radicals with enzyme substrate in the catalytic reaction system. A SWCNTs@MoS 2 catalysis-based colorimetric strategy was further proposed for the quantitative analysis of GSH with the concentrations linearly ranging from 0.01 to 1000.0 μM. Besides, the feasibility of the developed colorimetric method was evaluated by monitoring GSH separately in the extractions from hela cells and human serum, promising the extensive applications for monitoring various biological species like GSH in the clinical laboratory. Importantly, such a fabrication route for nanozyme with 2D/1D heterostructure may pave the way towards the wide applications for designing various nanzymes with improved catalysis. [Display omitted] • A nanozyme with 2D/1D heterostructure was synthesized by in-situ growing MoS 2 nanosheets on SWCNTs forming SWCNTs@MoS 2. • The SWCNTs@MoS 2 can exhibit greatly improved catalysis performances due to the formed 2D/1D interfacial coupling in the heterostructure. • SWCNTs@MoS 2 with 2D/1D heterostructure may possess enhanced charge transfer and more active sites during the catalytic reaction on the improved catalysis. • The competing reaction between GSH and chromogenic substrate triggered by the hydroxyl radical could be revealed toward the highly selective detection of GSH. • The SWCNTs@MoS 2 catalysis-based colorimetric strategy enables the evaluation of GSH in the extractions of hela and human serum with pretty high sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

Nanozymes are more stable, economical, and easier to produce than natural enzymes; however, their low activity in non-acidic environments and lack of substrate selectivity severely limit the applications of nanozymes. In this study, we developed Co- and N-doped carbon dot nanozymes (CoNCDs) that specifically exhibited peroxidase-like activity toward o-phenylenediamine in a non-acidic environment. Based on the peroxidase-like activity and fluorescence property of CoNCDs in a neutral environment, a one-pot multi-mode sensing platform (colorimetric and ratiometric fluorescence imaging) was developed to detect cholesterol and xanthine in solution and human serum samples. This platform was simple to operate, and the CoNCDs demonstrated a reduced detection time and an improved analytical performance compared to most of the reported nanozymes. Moreover, the improved peroxidase activity at neutral pH, good biocompatibility, and photostability of CoNCDs facilitated their use for monitoring endogenous H 2 O 2 levels in vivo. This study not only provides a novel approach for developing an acid pH-independent and substrate selectivity nanozyme but also demonstrates the application of ratiometric fluorescence imaging using the developed CoNCDs both in vitro and in vivo. [Display omitted] • CoNCDs showed the peroxidase-like activity at neutral and alkaline pH. • CoNCDs showed the substrate selectivity toward OPD, but no activity toward TMB and ABTS. • The one-pot multi-mode sensing platform for cholesterol and xanthine were developed. • CoNCDs was firstly applied to monitor H 2 O 2 in vitro and in vivo. [ABSTRACT FROM AUTHOR]