A signal-amplified electrochemical immunosensor for the detection of sulfadimidine in crayfish using COOH-MWCNTs-Fe3O4-GO nanohybrids modified working electrode

The label-free immunosensing technique is highly valued for its sensitivity and specificity, and advantages of simple preparation, fast detection (one-step), and rapid signal response. However, the sensitivity, stability, and specificity of this technique not only depend on the performance of antibodies, but also on the immunosensing interface of the bare glassy carbon electrode (GCE). This includes factors such as electrical conductivity, biocompatibility, and antibody loading capacity. In this study, carboxyl multiwalled carbon nanotubesferrosoferric oxide-graphene oxide (COOH-MWCNTs-Fe3O4-GO) was screened as the modified material of GCE to create an ideal immunosensing interface for the biological reaction between antibody-sulfadimidine (antiSM2) and SM2. The structure of both nanomaterials and the immunosensor were characterized. The nanohybrid exhibited a uniform interwoven structure of laminar and tubular components. This unique structure allows for a higher capacity for antibody loading. Based on this, a novel electrochemical immunosensor was constructed using COOH-MWCNTs-Fe3O4-GO/GCE, which exhibited a high anti-SM2 loading capacity and a rapid detection time of 30 min. The immunosensor exhibited a linear detection range of 0.01-100 ng/mL for SM2, with a limit of detection (LOD) of 0.003 ng/mL and a limit of quantification (LOQ) of 0.01 ng/mL. Additionally, satisfactory recoveries ranging from 94.40% to 109.00% were achieved in crayfish samples, with a relative standard deviation (RSD) of 4.97-8.64%. A novel immunosensors for highly sensitive detection of SM2 has been developed, which may provide an alternative idea for determination of SM2 in crayfish and other seafood.