Pd/Cu-TCPP(Fe)-polydopamine mediated magnetic relaxation switching immunosensor for sensitive detection of...

This study presents the development of a magnetic relaxation switching (MRS) immunosensor for the sensitive detection of chlorpyrifos (CPF) with a signal amplification strategy using Pd/Cu-TCPP(Fe) hybrid nanosheets and polydopamine (PDA). Pd/Cu-TCPP(Fe) nanosheets, which exhibit high peroxidase-like activity and excellent storage stability, making them suitable replacements for natural enzymes in biosensors, are further functionalized with goat anti-mouse IgG (Ab₂) to construct an immunosensor. The mechanism relies on the competition between free CPF and the immobilized bovine serum albumin-CPF conjugates for antibody binding, which modulates the aggregation of magnetic nanoparticles (MNPs) that are related to the transverse relaxation time. The optimized immunosensor shows a linear detection range from 0.5 ng/mL to 100 ng/mL and a limit of detection (LOD) of 0.24 ng/mL, outperforming traditional enzyme-linked immunosorbent assay (ELISA) methods by achieving an LOD that is about 9 times lower. Real sample analysis demonstrates the applicability of the Pd/Cu-TCPP(Fe)-PDA-MRS immunosensor for detecting CPF residues in tomato and water samples, with results well consistent with those obtained using gas chromatography. This work highlights the potential of nanomaterials in enhancing the performance of MRS immunosensors for pesticide residue analysis in environmental and food safety monitoring.