This study developed an electrochemical sensor for the nonenzymatic detection of paraoxon-ethyl using a glassy carbon electrode (GCE) modified with gold-silver core-shell (Au–Ag) nanoparticles combined with a graphene/poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) composite. The Au–Ag core-shell nanoparticles were synthesized using a seed-growth method and characterized by UV–vis spectroscopy and high-resolution transmission electron microscopy (HR-TEM). The composite of Au–Ag core-shell/graphene/PEDOT:PSS was characterized using infrared spectroscopy, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS). The sensor demonstrated good electrochemical and electroanalytical performance, showing a linear range of 0.2 to 100 μM, a limit of detection of 10 nM, and a sensitivity of 3.24 μA μM⁻¹ cm⁻² at pH 7. The sensor exhibited good reproducibility and selectivity, with no significant interference from several interfering species. It was also successfully applied to the determination of paraoxon-ethyl in real samples (Chinese cabbage and pear fruit) with results comparable to those obtained by standard spectrophotometric techniques. This sensor has potential for practical applications in pesticide detection.This study developed an electrochemical sensor for the nonenzymatic detection of paraoxon-ethyl using a glassy carbon electrode (GCE) modified with gold-silver core-shell (Au–Ag) nanoparticles combined with a graphene/poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) composite. The Au–Ag core-shell nanoparticles were synthesized using a seed-growth method and characterized by UV–vis spectroscopy and high-resolution transmission electron microscopy (HR-TEM). The composite of Au–Ag core-shell/graphene/PEDOT:PSS was characterized using infrared spectroscopy, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS). The sensor demonstrated good electrochemical and electroanalytical performance, showing a linear range of 0.2 to 100 μM, a limit of detection of 10 nM, and a sensitivity of 3.24 μA μM⁻¹ cm⁻² at pH 7. The sensor exhibited good reproducibility and selectivity, with no significant interference from several interfering species. It was also successfully applied to the determination of paraoxon-ethyl in real samples (Chinese cabbage and pear fruit) with results comparable to those obtained by standard spectrophotometric techniques. This sensor has potential for practical applications in pesticide detection.