Highly selective detection and differentiation of aminophenol isomers based on a bimetallic metal–organic-framework with peroxidase-like activity

Nanozymes, which possess similar catalytic activities to natural enzymes, are considered promising alternatives to natural enzymes. In the present study, a new bimetallic Fe/Mn metal–organic framework (MOF) nanomaterial was synthesized by doping Mn in MIL-101(Fe). Despite the low doping amount of Mn, the Fe/Mn MOF displayed remarkably enhanced peroxidase-like activity, catalyzing the conversion of chromogenic substrate ABTS to blue-green ABTS˙+. Subsequently, the addition of environmental pollutant aminophenol isomers induced different color changes in a solution, which provided a simple and feasible approach to differentiate them by the naked eyes. Based on the effect of aminophenol isomers on the absorption spectrum of ABTS˙+, colorimetric methods were developed to quantitatively determine m-AP and p-AP with detection limits of 0.13 μM and 0.20 μM, respectively. Furthermore, taking advantage of a smart phone software-color recognizer to analyze the RGB value, a rapid detection method for m-AP was proposed, offering a solution to detect m-AP in the absence of any analytical instruments. This work verified the essential role of doping Mn in enhancing the enzyme-like activity of nanozymes. Simultaneously, the proposed simple, rapid, and accurate sensing method provided a new option to differentiate and determine aminophenol isomers, which has great potential for environmental application.