Mucosal-associated invariant T (MAIT) cells exhibit significant potential in the assessment of tumor development and immunotherapy. However, there is currently no convenient and efficient method to analyze the quantitative changes of MAIT cells during cancer development and treatment, which has not been extensively studied. Here, we report an electrochemical biosensor designed to efficiently monitor MAIT cells in peripheral blood by simultaneously recognizing Vα7.2 and CD161 on MAIT cells. Natural red blood cell membrane, tetrahedral DNA nanostructure, and modified nanometal framework are selected as antifouling coating, antibody scaffold, and electrochemical probe, respectively. Owing to the synergistic effects of these materials, the biosensor achieves robust antifouling ability while maintaining excellent detection performance using rapid differential pulse voltammetry. We show a decrease in the number of MAIT cells in peripheral blood associated with aging and the development of mucosa-associated tumors. Our research has prospects in assessing the degree of malignancy of tumors, distinguishing immunotherapy responses in patients, reducing costs, and promoting the transformation of electrochemical sensing technology into clinical settings.