Highly sensitive and label-free detection of the biomarker carbohydrate antigen 15-3 (CA 15-3) remains a challenge in the diagnosis of breast cancer. Here, a novel electrochemical immunosensor capable of sensitive and label-free detection of CA 15-3 is reported. This unique immunosensor, equipped with a highly conductive graphene (i.e., N-doped graphene sheets)-modified electrode, exhibited significantly increased electron transfer and high sensitivity toward CA 15-3. This novel immunosensor, with a low detection limit of 0.012 U/mL, worked well over a broad linear range of 0.1-20 U/mL. Unlike conventional immunosensors, which usually involve complicated label processing and time-consuming separations, the use of highly conductive graphene avoids the need for labels and is simple in nature. The strategy developed for this immunosensor provides a promising approach for clinical research and diagnostic applications.
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