Sensitive electrochemical immunoassay for chlorpyrifos by using flake-like Fe3O4 modified carbon nanotubes as the enhanced multienzyme label

• A three-dimensional immune platform was built with polydopamine nanospheres.
• Flake-like Fe3O4@carbon nanotubes was prepared for making multienzyme labels.
• Novel immunoassay of chlorpyrifos was achieved with a detection limit of 6.3 pg/mL.

A highly sensitive electrochemical immunoassay of chlorpyrifos (CPF) was developed by using a biocompatible quinone-rich polydopamine nanospheres modified glass carbon electrode as the sensor platform and multi-horseradish peroxidase-flake like Fe3O4 coated carbon nanotube nanocomposites as the signal label. Due to the quinone-rich polydopamine nanospheres, the platform exhibited excellent fixing capacity by simple coating of sticky polydopamine nanospheres and subsequent oxidization. By coprecipitation of Fe3+ and Fe2+ on polydopamine modified carbon nanotubes (CNTs) with the aid of ethylene glycol (EG), the flake-like Fe3O4 coated CNTs (CNTs@f-Fe3O4) were synthesized and chosen as the carrier of multi-enzyme label due to the high loading of secondary antibody (Ab2) and horseradish peroxidase (HRP) and also the peroxidase-mimic activity of Fe3O4. Under the optimum conditions, the immunosensor can detect CPF over a wide range with a detection limit of 6.3 pg/mL. Besides, the high specificity, reproducibility and stability of the proposed immunosensor were also proved. The preliminary application in real sample showed good recoveries, indicating it holds promise for fast analysis of CPF in aquatic environment.

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