Gold nanoparticle‐carbon nanotube nanohybrids with peroxidase‐like activity for the highly‐sensitive immunoassay of kanamycin in milk

Summary Owing to the increasing incidences of antibiotic residues being found in foods of animal‐origin, rapid and reliable screening methods for detecting these residues are urgently required. This study aimed to develop a robust and ultrasensitive colorimetric immunoassay based on nanohybrids for the rapid screening of kanamycin (KAN) residues in milk. The HAuCl 4 solution was directly reduced on the multiwalled carbon nanotubes (MWCNTs) using a one‐step synthesis method to obtain the Au/MWCNTs nanohybrids. The Au/MWCNTs exhibited mimetic peroxidase activity and higher affinities for the TMB and H 2 O 2 compared with horseradish peroxidase and other nanohybrids. A direct competitive enzyme‐linked immunosorbent assay (dcELISA) based on Au/MWCNTs was developed and employed for KAN detection in milk samples under optimised conditions. The dcELISA showed high sensitivity toward KAN residues, with a detection limit of 11.2 pg/mL. Moreover, this novel immunoassay displayed high precision and accuracy in milk samples, with a recovery rate ranging from 94.3 to 124.5% and a coefficient variation from 7.8 to 11.3%. Eight real milk samples were found to contain a KAN concentration in the range of ND–0.26 ng/mL. Therefore, this dcELISA based on the Au/MWCNTs nanohybrid has promising potential for applications in food monitoring and quality control.