Ultrasensitive electrochemical immunoassay for squamous cell carcinoma antigen using dumbbell-like Pt-Fe₃O₄ nanoparticles as signal amplification.

Dumbbell-like Pt-Fe₃O₄ nanoparticles (NPs) were synthesized and used as a novel kind of label for the preparation of electrochemical immunosensor, which is applied to the detection of cancer biomarker squamous cell carcinoma antigen (SCC-Ag). The signal amplification strategy, using the synergetic effect present in Pt-Fe₃O₄ to increase the reduction ability of the NPs toward H₂O₂, improved the sensitivity of the immunosensor. Nitrogen-doped graphene sheets (N-GS) were synthesized from graphite oxides through thermal annealing of graphite oxides in ammonia, which was used to immobilize primary anti-SCC antibody (Ab₁). Secondary anti-SCC antibody (Ab₂) was adsorbed onto the Pt-Fe₃O₄ NPs. The immunosensor was prepared through a sandwich structure and displayed a wide linear range (0.05-18 ng/mL), low detection limit (15.3 pg/mL), good reproducibility and stability. The method has been applied to the analysis of clinical serum samples with satisfactory results. These labels for immunosensors can provide many potential applications for the detection of different biomolecules.