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An electrochemical immunosensor for quantitative detection of α-fetoprotein (AFP) in human serum was developed using graphene sheets (GS) and thionine (TH) as electrode materials and mesoporous silica nanoparticles (MSNs) loaded with ferroferric oxide (Fe3O4) nanoparticles and horseradish peroxidase (HRP) as labels for signal amplification. In this study, the compound of GS and TH (GS-TH) was used as a substrate for promoting electron transfer and immobilization of primary antibody of AFP (Ab1). MSNs were used as a carrier for immobilization of secondary antibody of AFP (Ab2), Fe3O4, and HRP. The synergistic effect occurred between Fe3O4 and HRP and greatly improved the sensitivity of the immunosensor. This method could detect AFP over a wide concentration range from 0.01 to 25 ng ml(-1) with a detection limit of 4 pg ml(-1). This strategy may find wide potential application in clinical analysis or detection of other tumor markers., (Copyright © 2014 Elsevier Inc. All rights reserved.)

For the specificity of prostate cancer markers, prostate specific antigen (PSA) has been widely used in prostate cancer screening, diagnosis, and treatment after monitoring. In normal male serum, PSA can only be detected in traces of 0-4 ng mL(-1). In this paper, we constructed an electrochemical immunosensor for PSA detection using a nanocomposite film of graphene sheets-methylene blue-chitosan (GS-MB-CS) as electrode material. The nanocomposite film showed high binding affinity to the electrode and was used to immobilize the antibody of PSA. The modification procedure was monitored by cyclic voltammetry (CV). An amperometric biosensor was easily developed based on the response of peak current to the capture of PSA induced by specific antigen-antibody reactions. Under optimum conditions, the amperometric signal decreased linearly with PSA concentration (0.05-5.00 ng mL(-1)). A low limit of detection (13 pg mL(-1)) and a high selectivity are obtained. Moreover, the prepared immunosensor was applied for the analysis of PSA in serum samples with satisfactory results. The proposed method may have a promising future in biochemical assays for high selectivity, good reproducibility, and stability., (Copyright © 2012 Elsevier Inc. All rights reserved.)