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NADH oxidase (NOX) is an oxidoreductase that catalyzes the oxidation of NADH to NAD+ with the participation of oxygen. NOX can artificially regulate metabolic processes as an important regulatory enzyme for NAD+ regeneration. In this study, cobalt-doped molybdenum sulfide (Co-MoS2) nanocomposite was prepared by hydrothermal synthesis, which exhibited NOX mimics. The catalytic mechanism of NOX mimics was studied. The NOX-like activity of Co-MoS2 is optimal at pH 4.5 and in the temperature range of 20–45℃. Further, its catalytic activity maintained almost the same after 5 cycles of repetitive addition of NADH, suggesting that Co-MoS2 nanozyme possessed significant catalytic persistence. The produced H2O2 catalyzed by Co-MoS2 can be detected by horseradish peroxidase (HRP) and 3,3′,5,5′-tetramethylbenzidine at pH4.5. Thus, interestingly, a colorimetric NADH sensor was proposed on the basis of the enzymatic cascade reaction of NADH oxidase-like conjugated with HRP. This as-established method had wide detection range (0.5–800 μM) with the detection limit of 0.25 μM NADH, capable of detecting NADH in real sample.

A simple colorimetric sensing strategy for Hg2+ ions was developed using silver/copper nanoclusters (Ag/Cu NCs) with excellent selectivity and sensitivity. Bimetallic Ag/Cu NCs were synthesized by using glutathione (GSH) as a template and sodium borohydride as a reducing agent. It was found that the peroxidase-like activity of Ag/Cu NCs was significantly enhanced in the presence of Hg2+. Therefore, a colorimetric method based on catalysis was developed to detect Hg2+ with a linear concentration range of 0.1–700 nM and a detection limit of 0.05 nM (S/N = 3). The common species have no effect on Hg2+ ion detection. Furthermore, this method is applicable to accurately detect Hg2+ in real aqueous samples and is reproducible. Therefore, owing to the merits of sensitivity, selectivity, rapid response and visual read-out, it can be promising in the development of a portable Hg2+ analyzer for on-site detection.

A simple colorimetric sensing strategy for Hg

Nanozymes featuring with favorable activity, good stability and easy scale-up production, are promising to replace natural enzymes for various applications. However, it remains a challenge to explore the cascade reactions of multi-enzyme mimics, aiming at synergistic catalysis for various applications. Herein, vanadium nitride nanoparticles deposited on carbon nanofibers (VN@CNFs) composite was facilely prepared by typical electrospinning route with subsequently ammonia reduction process. The nanocomposite showed excellent peroxidase (POD)-like and superoxide dismutase (SOD)-like activities. Additionally, their catalytic mechanisms were systematically researched. Coupling of SOD-like with POD-like as cascade enzyme, a selective and sensitive colorimetric detection of superoxide anion (O

Nanozymes are artificial enzymes, which can substitute natural enzymes for wide range of catalysis-based applications. However, it is challenging to explore novel mimic enzymes or multi-enzyme mimics. Herein we report the facile preparation of uniform CuS nanoclusters (NCs), which possessed outstanding tetra-enzyme mimetic catalytic activities, including peroxidase (POD)-mimics, catalase (CAT)-mimics, ascorbic acid oxidase (AAO)-mimics and superoxide dismutase (SOD)-mimics. The catalytic mechanism of POD-like was coming from the oxygen vacancies of CuS. Furthermore, the steady-state kinetics of POD-, CAT- and AAO mimics of CuS NCs were systematically explored. On basis of the enzymatic cascade reaction that acid phosphatase (ACP) involved in a weak acidic environment, in the presence of O-phenylenediamine, quinoxaline fluorescent substance will be generated. Thus, a fluorescent biosensor platform was proposed for detection of ACP with the linear range of 0.05–25 U L−1 and limit of detection of 0.01 U L−1. The as-proposed method was applicable to real serum sample detection accurately and reproducibly. Considering the simple preparation, good stability, excellent multi-enzyme activities and controllable experimental operation, CuS NCs would provide a basis for expanding to other biocatalytic and biomedical applications.