Design of colorimetric sensors based on 3D graphene aerogel/Co₃O₄ nanowires and enzyme inhibition principles

Parathion-methyl, a widely used pesticide in agricultural production, poses significant risks to human immune health when present in excessive amounts in water and soil. Sensitive and rapid detection of parathion-methyl in environmental and agricultural samples is thus critical. Conventional methods like gas chromatography (GC) and liquid chromatography-mass spectrometry (LC-MS) rely on large-scale instrumentation, offering high sensitivity but suffering from limitations including complex sample pretreatment, cumbersome operations, and high costs. These drawbacks underscore the need for efficient, cost-effective, and user-friendly analytical approaches.Colorimetric sensors, enabling naked-eye detection of analytes in biological and environmental samples, have gained traction due to their low cost, simplicity, and rapid response. In such systems, the catalytic activity of artificial enzymes (nanozymes) is pivotal for inducing colorimetric reactions. Nanozymes, which mimic natural enzymes with enhanced stability and tunable catalytic properties, have emerged as promising alternatives. A key challenge remains enhancing peroxidase-mimetic activity while devising innovative detection strategies to enable visual pesticide residue monitoring in agricultural products.Cobalt oxide (Co₃O₄), a nanozyme exhibiting both catalase-like and peroxidase-like activities, benefits from a higher reduction potential of Co(III)/Co(II) (1.92 eV) compared to other metal ions. However, its catalytic efficiency often diminishes due to agglomeration during synthesis, caused by magnetic interactions and van der Waals forces. To address this, graphene aerogels (3D GAs) were integrated as scaffolds. Their robust mechanical strength, electrical conductivity, and three-dimensional (3D) interconnected architecture provide a stable matrix for nanozyme loading and facilitate rapid catalytic reactions.This study introduces a 3D GA/Co₃O₄ nanowire-based visual sensor for parathion-methyl detection. The composite was synthesized via a one-pot hydrothermal method, yielding enhanced peroxidase-mimetic activity toward 3,3',5,5'-tetramethylbenzidine (TMB) substrate compared to pristine Co₃O₄. By leveraging the peroxidase-like activity of 3D GA/Co₃O₄ and the inhibitory effect of organophosphorus pesticides on acetylcholinesterase (AChE), a colorimetric sensor was developed. The system demonstrated a linear response to parathion-methyl within 30–1000 nmol/L, with a detection limit of 10 nmol/L. This work pioneers the use of graphene aerogels as sensitizers to boost peroxidase-mimetic activity and offers a scalable platform for visual pesticide monitoring.