<p>A label-free electrochemical immunosensor for carcinoembryonic antigens (CEA) detection is reported based on a built-in thiol-mesoporous carbon architecture. The material was functionalized with 3-maleimidepropionic acid to immobilize anti-CEA antibodies. The immunosensor was characterized using field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. Biorecognition events were monitored by differential pulse voltammetry, with current intensity dependent on protein concentration. The device exhibited a linear range of 1–10 ng mL^-1 for CEA, with a clinically relevant limit of detection of 1.02 ng mL^-1. The immunosensor successfully detected CEA in human serum samples, with results comparable to those obtained by a standard spectrophotometric method. This platform has proven to be a promising alternative for the prognosis and management of patients with colorectal cancer, as well as having significant potential for point-of-care diagnosis.</p> Graphical Abstract <p></p>