Label-free immunosensor based on Au@Ag2S nanoparticles/magnetic chitosan matrix for sensitive determination of ractopamine

• Electrochemical biosensor based on Au@Ag2S is developed for the first time.
• The as-prepared matrix enhanced the loading capacity and stability of the biomolecules.
• The proposed label-free immunosensor has a wide linear range and low detection limit.

A label-free electrochemical immunosensor for sensitive determination of ractopamine (RAC) based on Au@Ag2S core@shell nanoparticles/magnetic chitosan/thionine matrix film (CSMCM) was simply fabricated. The CSMCM not only enhanced the loading capacity of the biomolecules and stability of the immunosensor by covalently immobilizing due to stable conjunction between S-bond of Ag2S shell and NH2-bond of biomolecules, but also provided a favorable microenvironment to maintain the activity of the immobilized biomolecules due to the excellent biocompatibility of magnetic chitosan. Thionine was fabricated into the matrix to increase the conductivity of the CSMCM. All contributions of the CSMCM observably increased the sensitivity and stability of the immunosensor compared with other references. Performance of the immunosensor was evaluated in terms of its detection limit, sensitivity, pH, time and temperature of incubation, selectivity, reproducibility, and stability in a lab setting. Under optimal conditions, the fabricated immunosensor in this work exhibited a linear response with RAC in the concentration range of 0.01–10 ng mL−1, with the low detection limit of 2.5 pg mL−1 (S/N = 3).