Herein, a colorimetric platform is presented based on zirconium-doped cobalt oxyhydroxide (Zr-CoOOH) nano-enzymes for the rapid detection of malathion (MAL). The CoOOH nano-enzymes showed excellent oxidase-like activity. With the use of 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate, the Zr-CoOOH nano-enzymes can oxidize the colorless TMB to the blue product (oxTMB), and the UV-visible spectral absorption band of oxTMB is 652 nm. The oxidase-like activity of Zr-CoOOH nano-enzymes was significantly enhanced, which was attributed to the high affinity between Zr-CoOOH nano-enzymes and TMB. The metal in the Zr-CoOOH nano-enzymes can be combined with the phosphate thiolate groups in the MAL molecule, thus inducing an enhanced catalytic activity of MAL for the reaction. The Zr-CoOOH+TMB+MAL system can achieve the quantitative detection of MAL. Under the optimized conditions, the constructed sensor exhibited a linear relation with MAL over the range of concentration from 0.1-10 μM, with a detection limit of 0.023 μM. The sensing platform showed excellent anti-interference and batch stability. This strategy expands the application of nano-enzymes to the area of rapid detection.

In this work, a novel bifunctional zirconium dioxide@zeolitic imidazolate framework-90 (ZrO₂@ZIF-90) nanozyme was successfully developed for the catalytic degradation and electrochemical detection of methyl parathion (MP). The ZrO₂@ZIF-90 nanozyme with phosphatase hydrolysis activity can convert MP into p-nitrophenol (p-NP). The addition of ZrO₂ riched in Lewis acid Zr(Ⅳ) sites significantly enhanced the phosphatase hydrolysis activity of ZIF-90. ZrO₂@ZIF-90 also displayed satisfactory electrocatalytic performance on account of the high surface area, high porosity and powerful enrichment ability of the ZIF-90 and the excellent ion transfer capacity of ZrO₂. A ZrO₂@ZIF-90 nanozyme modified glassy carbon electrode (ZrO₂@ZIF-90/GCE) was then fabricated to analyze p-NP formed through MP degradation. Under the optimized conditions, the developed sensor displayed satisfactory analytical performance with a low limit of detection of 0.53 μmol/L and two wide linear ranges (3-10 and 10-200 μmol/L). ZrO₂@ZIF-90 nanozyme accomplished to the degradation and electrochemical detection of MP in river water and spiked fruits. This study identifies a promising new strategy for the design of bifunctional nanozymes for the detection of environmental hazards.