AuNSs@Ag Nanoprobe-based dual-mode sensor for rapid and sensitive detection of dimethoate

Dimethoate (DMT), an organophosphate pesticide, is extensively employed in agriculture for pest management, however its persistent residues raise critical concerns regarding human health and environmental safety, necessitating the development of reliable quantification methods for residual monitoring. The sensor utilizes silver-coated gold nanostructures (AuNSs@Ag), which possess bimetallic properties and intrinsic peroxidase-like activity, to catalyze the H₂O₂-mediated oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). This reaction results in the formation of a blue oxidation product (ox-TMB), producing a distinct colorimetric signal. Simultaneously, this reaction generates a characteristic SERS fingerprint spectrum of ox-TMB. However, upon the introduction of DMT, competitive adsorption occurs between DMT and TMB for the active sites on the surface of AuNSs@Ag, resulting in a reduction of the reactive sites on AuNSs@Ag and a decrease in its peroxidase-like activity. Consequently, the formation of ox-TMB is reduced, leading to a diminished transition from the colorless to the blue state, as well as a weakened SERS signal. Therefore, this dual-mode probe enables specific and highly sensitive detection of DMT. The limit of detection (LOD) for DMT was determined to be 6.76 μg/L using the colorimetric method and 1.19 μg/L using the SERS method. In real sample applications, such as in apples and celery, the recovery rates ranged from 88.33 % to 116.67 %, with relative standard deviations (RSD) below 5 %. This dual-mode sensor offers a simple, rapid, and cost-effective approach for on-site detection of DMT, presenting significant potential for applications in food safety monitoring and environmental protection.