Ultrasensitive immunosensor for the detection of cancer biomarker based on graphene sheet

An ultrasensitive electrochemical immunosensor based on graphene sheet (GS) has been developed. GS was used to immobilize mediator thionine (TH), horseradish peroxidase (HRP) and secondary anti-prostate-specific antigen (PSA) antibody (Ab2) and the resulting nanostructure (GS-TH-HRP-Ab2) was used as the label for the immunosensor. With primary anti-PSA antibody (Ab1) also immobilized onto the GS, the immunosensor displayed a wide range of linear response (0.002-10 ng/mL), low detection limit (1 pg/mL), good reproducibility, selectivity and stability. The good performance of the immunosensor is attributed to the graphene sheet's high surface-to-volume ratio which allows the immobilization of a high-level of Ab1, Ab2, TH and HRP and its good electrical conductivity which can improve the electron transfer among TH, HRP, H2O2 and electrode. The immunosensor was used to detect the PSA contents in serum samples from patients and satisfactory test results were obtained in comparison with the ELISA test results. Thus, graphene-based labels may provide many potential applications for the detection of different cancer biomarkers.