The nanozyme-based strategy is currently one of the frontiers in the detection of toxic heavy metal ions. However, the utilization of noble metal free nanozymes to construct an economically and environmentally sustainable methodology remains largely unknown. Here, chitosan-functionalized molybdenum(IV) selenide nanosheets (CS-MoSe 2 NS), greenly synthesized by an ionic liquid-assisted grinding method, were exploited for the colorimetric sensing of mercury ions (Hg 2+ ). The sensing principle was based on the activating effect of Hg 2+ on CS-MoSe 2 NS nanozyme activities, triggered by the in situ reduction of chitosan-captured Hg 2+ ions on a MoSe 2 NS surface. Using 3,3′,5,5′-tetramethylbenzidine (TMB) as a colorimetric indicator, the concentrations of activator-like Hg 2+ ions could be quantitatively and selectively monitored, reaching a limit of detection of 3.5 nM with the ultraviolet−visible spectrophotometer. In addition, the integration system of CS-MoSe 2 NS with a smartphone achieved a portable detection limit as low as 8.4 nM Hg 2+ within 15 min and showed high specificity and anti-interfering ability over other ions and great practicability in real water and serum samples. The eco-friendly properties of such sensing system were also confirmed. This work emphasizes the rational portable assembly of biocompatible nanozymes like CS-MoSe 2 NS for the field detection of Hg 2+ in food, biological, and environmental samples.
Enzyme-like metal–organic
frameworks (MOFs) are currently
one type of starring material in the fields of artificial enzymes
and analytical sensing. However, there has been little progress in
making use of the MOF structures based on the catalytically active
metal center with multiple valences. Herein, we report a mixed-valence
Ce-MOF (Ce-BPyDC) that can exhibit both oxidase-like and peroxidase-like
activities. Ce-BPyDC was synthesized by a facile hydrothermal method,
which preserves the rare coexistence of Ce(III) and Ce(IV) in the
MOF structure. The enzymatic studies demonstrated the enzyme-like
activities of Ce-BPyDC follow the Michaelis–Menten kinetics
and are strongly dependent on temperature, pH, and reaction time.
Ce-BPyDC was also revealed to exert high catalytic activity that could
transcend horseradish peroxidase and other MOF nanozymes, due to the
redox-active Ce(III)/Ce(IV) cycles inside. Furthermore, the simple
synthesis, high nanozyme activity, and great stability of Ce-BPyDC
motivated us to establish a colorimetric biosensing platform using
3,3′,5,5′-tetramethylbenzidine as a color reagent. Adopting
this strategy, we established a visual, sensitive, and selective colorimetric
method for ascorbic acid (AA) detection, for which the linear interval
and limit of detection were 1–20 and 0.28 μM, respectively.
The successful AA detection in real juice samples implies the promising
use of such mixed-valence MOF nanozymes in food and biomedical samples.
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