Thiol-Functionalized Magnetic Biochar-Mediated Matrix Cleanup and Selective Enrichment for Trace-Level Rapid Determination of Cadmium in Environmental Water and Aquatic Products.

Efficient enrichment and rapid determination of trace cadmium (Cd2+) in complex environmental and food matrices remain challenging because of severe matrix interference and insufficient sample pretreatment efficiency. Herein, a thiol-functionalized silica-coated magnetic biochar (MBC@SiO2-SH) was developed as a selective magnetic adsorbent and integrated with a homogeneous chemiluminescence immunoassay (CLIA) to establish an enrichment-assisted analytical strategy for trace Cd2+ determination in environmental water and aquatic products. Owing to its abundant thiol coordination sites, large specific surface area, and excellent magnetic responsiveness, MBC@SiO2-SH exhibited a high practical Cd2+ enrichment capacity (82.65 mg/g) under high-loading conditions, remarkable selectivity, and good reusability toward Cd2+. Adsorption kinetic, isotherm, thermodynamic, and X-ray photoelectron spectroscopy analyses revealed that Cd2+ uptake was predominantly governed by Cd-S coordination accompanied by physical adsorption. Under the optimized fixed-bed enrichment conditions, the proposed column achieved a preconcentration factor of approximately 40, enabling efficient matrix cleanup and selective enrichment prior to CLIA. The integrated method exhibited excellent analytical performance for both environmental water and aquatic products, with recoveries of 92.26-118.64% and 92.41-108%, respectively, and showed good agreement with ICP-MS. By coupling selective magnetic preconcentration with rapid homogeneous immunodetection, the proposed strategy provides a simple, sensitive, and efficient analytical platform for routine monitoring of trace Cd2+ and offers a generalizable framework for enrichment-assisted rapid analysis of trace contaminants in complex environmental and food matrices.