Silver-nanoparticle-coated Fe₃O₄/chitosan core-shell microspheres for rapid and ultrasensitive detection of thiram...

We report a surface magnetic solid-phase extraction-surface-enhanced Raman scattering (SMSPE-SERS) method based on silver-nanoparticle-coated Fe₃O₄/chitosan (Fe₃O₄/CS@Ag) microspheres as the substrate, and this method integrates all steps from sample pretreatment to detection. Fe₃O₄/CS was synthesized by a one-step solvothermal method in which chitosan (CS) was used as a surface modifier and adsorbent. Fe₃O₄/CS@Ag microspheres exhibit both adsorption ability and SERS activity. Therefore, we used the SMSPE-SERS method to detect pesticide residues on fruit peel. The procedures of capturing, separating and enriching pesticides, as well as detection, are all integrated. In addition, the SERS substrate allows label-free detection of thiram pesticide in both fruit peel and apple juice. Owing to the uniform distribution of Ag NPs and the adsorption ability of CS, the thiram-detection sensitivity was sufficiently high to detect the lowest concentration of 1.2 ng/cm², which was significantly lower than the maximum thiram residue limit (7 μg/cm²) in fruits. The method was comparable to high-performance liquid chromatography with recovery ranging from 86.60 to 109.69 %.