Ultrasensitive enzyme-free immunoassay for squamous cell carcinoma antigen using carbon supported Pd–Au as electrocatalytic labels

• N-dopedgraphene sheets add the loading capacity of primary antibody.
• Pd–Au/C nanocrystals facilitate the decomposition of H2O2.
• Sandwich-typeimmunoreactions are used to detectsquamous cell carcinoma antigen.
• The immunosensorhasa low detection limit.

A novel nonenzymatic sandwich-type electrochemical immunosensor has been developed to detect squamous cell carcinoma antigen (SCCA). Nitrogen-doped graphene sheet (N-GS) was used to increase capacity of capturing primary antibodies (Ab1). Carbon-supported Pd–Au binary nanoparticles (Pd–Au/C) were synthesized and used to label secondary antibodies (Ab2). The specific binding of SCCA and antibodies enabled a quantitative attachment of Pd–Au/C on the electrode surface. Electrocatalytic analysis showed that the prepared Pd–Au/C exhibit excellent electrocatalytic activity towards hydrogen peroxide (H2O2). We use current response of electrocatalytic labels Pd–Au/C to detect the concentration of SCCA. The unique nonenzymatic immunosensor exhibits a relatively wide linear range from 0.005 to 2 ng mL−1 and high sensitivity with a low detection limit of 1.7 pg mL−1. The immunsensor also shows good reproducibility (4.2%) and stability (5.8%), which makes it an enormous application prospect in clinical research.

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