Ultrasensitive Colorimetric Strategy Based on Ir Nanoparticles Anchored Hollow NiO/NiCo ₂ O ₄ Multishell Nanospheres for Acid Phosphatase and Malathion Detection in Vegetables

The detection of malathion in vegetables is of great significance for the environment, human health, and food safety. Here, Ir nanoparticles anchored on hollow NiO/NiCo2O4 multishell nanospheres (Ir@NiO/NiCo2O4) with peroxidase (POD)-like activity are constructed for colorimetric determination of acid phosphatase (ACP) and malathion. Owing to the Ir doping and unique hollow multishell structures, Ir@NiO/NiCo2O4 displays more active sites, a large specific surface area, and rapid mass transport, thus leading to high catalytic activity and reaction rate. Thanks to the remarkable POD-like activity and the inhibition effect of malathion on ACP activity, we propose a cascade catalytic signal amplification system toward ACP and malathion with low detection limits (LODs) of 3.9 mU/L and 9.53 ng/mL, respectively. Moreover, the Ir@NiO/NiCo2O4-based sensor exhibits excellent selectivity, stability, and repeatability, as well as satisfactory feasibility in real samples. This work aims to construct hollow multishell nanozymes with high activity and specificity, thus further developing nanozyme-based colorimetric biosensors.