Colorimetric determination of Hg based on the mercury-stimulated oxidase mimetic activity of AgPO microcubes.

Four kinds of AgPO materials were prepared by controlling the experimental conditions, which were developed as oxidase mimics. Experimental results showed that different synthesis methods led to distinct crystal structures, morphologies, and surface properties, which contributed to diverse oxidase-like activities of AgPO materials. Among them, AgPO microcubes (APMCs) can efficiently catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine in the presence of dissolved oxygen to form a blue-colored oxide, presenting the best intrinsic oxidase mimetic ability. The higher-energy [110] facets with more oxygen vacancies exposed and more active sites coupled with more negative charge and larger specific surface area of APMCs contributed to its enhanced oxidase mimetic performance. Besides, mercury ions were proved to remarkably and selectively stimulate the oxidase-like ability of APMCs owing to the formation of Ag-Hg amalgam on its surface. Based on the stimulating effect of Hg towards APMCs, a simple and rapid method for colorimetric determination of Hg was thus established via the significant signal amplification and megascopic color variation. Under the optimal conditions, the sensing system showed a good linear relationship ranging from 0.1 to 7.0 μM and a detection limit of 20 nM for Hg, exhibiting high selectivity and good colour stability. Moreover, the colorimetric method was successfully applied to determine Hg in real water samples. Considering these advantages, the developed colorimetric sensing system is expected to hold bright prospects for trace determination of Hg in biological, environmental, and food samples. Graphical abstract The preparation process of AgPO materials and Hg-stimulated enhanced oxidase-like ability of AgPO microcubes in catalyzing the oxidation of TMB to generate a typical blue color, which can be applied in rapid and ultrasensitive detection of Hg visually.