Facilely Fabricating Bimetallic Ir/Co Nanozymes with High Oxidize-like Activities for Sensitive Detection of Malathion with Portable Swabs

Bimetallic nanozymes not only have strong synergistic catalysis ability but also may improve the catalytic specificity of the nanozymes. Herein, the oxidase (OXD)-mimic Ir/Co bimetallic nanozymes were prepared through a coordination reaction between the Ir(III) complex with the 2-methylimidazole (MeIm) ligands in ZIF-67 under mild conditions without the pyrolysis and physical doping procedures. It is found that the trace amount of Ir-modified ZIF-67 (Ir@ZIF-67) possesses 18.17-fold that of catalytic ability and 7.86-fold that of the reaction rate as those of pristine ZIF-67. On the other hand, compared with ZIF-67, the OXD-like specificity of Ir@ZIF-67 has been increased 9.7%. The theoretical simulation shows that the high-performance of Ir@ZIF-67 comes from its higher O₂ adsorption ability. In virtue of the high performing OXD-like catalytic property, Ir/Co bimetallic nanozymes are employed to establish a simple and sensitive colorimetric pesticides detection platform without deleterious H₂O₂, which offers excellent "switch-on" malathion (MAL) detection in the linear range of 0.05-25 μM with a limit of detection (LOD) of 11.8 nM. Moreover, Ir/Co bimetallic nanozymes are successfully fabricated into the MAL test swabs. Assisted by a color-reading APP, the test swabs can detect MAL with the LOD as low as 18.5 nM. Surprisingly, such a simple test swab can achieve such high sensitivity for MAL detection. The real sample analysis verifies the high potential of the test swabs in practical application. The excellent performance of the fabricated test swabs can promote the formation of the situation where pesticides detection can be tested at any time and any place and can be carried out by anyone. This work not only provides a novel approach to designing polymetallic nanozymes but also displays the promising application of Ir/Co bimetallic nanozymes in the field of colorimetric sensing.