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We designed and synthesized iron doped CuSn­(OH)6 (Fe/CuSn­(OH)6) microspheres, which was selected as a nanoenzyme to detect hydrogen peroxide (H2O2), by a coprecipitation method for the first time. Significantly, Fe/CuSn­(OH)6 microspheres revealed the high peroxidase-like activity, which was evaluated using the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) catalytically oxidized by H2O2. Colorless TMB could be turned into oxidized TMB (oxTMB) with a blue color change in the process of oxidation. The catalytic reaction mechanism has been proved to be •OH, attributing to H2O2 decomposition. On the basis of the high peroxidase mimetic activity of Fe/CuSn­(OH)6 microspheres, a novel, simple, and sensitive H2O2 colorimetric detection system was successfully constructed. Experimental data revealed that the Fe/CuSn­(OH)6 microspheres nanoenzyme additionally demonstrated the high peroxidase-like activity compared with horseradish peroxidase. Furthermore, based on the Fe/CuSn­(OH)6, a rapid detection of H2O2 could be come true in the wide range (30–1000 μM) with a lower detection limit of 9.49 μM (S/N = 3). The feasibility of this convenient method was confirmed by qualitative detection of H2O2 residue in milk.

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In this paper, CoO nanotubes loaded on the surface of graphene oxide (GO) have been first modified by 5,10,15,20tetrakis(4-carboxyl phenyl)porphyrin (Por) by a hydrothermal method. Por/CoO/GO exhibits excellent peroxidase-like activity, which is evaluated by virtue of the chromogenic substrate 3,3,5,5tetramethylbenzidine (TMB). In the presence of H 2 O 2 , Por/CoO/ GO nanoperoxidase can rapidly catalyze colorless TMB to be oxidized into blue oxTMB, which is distinguished visually in 1 min. The experimental data including fluorescence and electrochemistry data and radical scavengers confirm that the catalytic mechanism of Por/CoO/GO is ascribed to electron transfer between substrates, as well as produced active species (h + and • O 2 − ). Based on Por/ CoO/GO nanoperoxidase, a fast colorimetric sensor for H 2 O 2 has been established for a wide range of concentrations (0.1−3 mM) with a lower limit of detection (LOD = 0.2942 mM). Notably, the blue color of oxTMB can be gradually faded in the presence of dopamine (DA) with various concentrations. Thus, a fast, cheap, and convenient colorimetric sensor has been designed to monitor DA in a wide range (0.2−10 μM) with a much lower LOD (0.1391 μM). The Por/CoO/GO-based colorimetric platform has been validated by determining DA in real serum samples.