Engineered LaBi₃O₆ nanosheet interface enabling robust and ultrasensitive detection of carcinoembryonic antigen

Cancer early detection demands highly sensitive, cost-effective, and reliable sensing platforms. Herein, we report the synthesis of lanthanum bismuth oxide nanosheets (LaBi₃O₆ NSs) via a simple sol-gel method and their innovative application in constructing a label-free electrochemical immunosensor for the detection of carcinoembryonic antigen (CEA). The LaBi₃O₆ NSs serve as an excellent matrix offering a large specific surface area, high conductivity, and rich active sites, significantly enhancing electron transfer and biomolecular immobilization. The fabricated immunosensor demonstrates outstanding analytical performance: a wide linear range from 0.1 to 1000 ng mL^-1, an ultra-low detection limit of 56.2 pg mL^-1, and high selectivity against common interferents. It also exhibits remarkable reproducibility (RSD < 5%) and stability (retaining 90% activity after 15 days). Practical applicability was confirmed through successful CEA detection in human serum samples, with recovery rates of 98.8-101.2% and excellent agreement with standard methods. This work not only presents a novel bismuth-based nanomaterial for biosensing but also provides a robust, eco-friendly, and highly efficient strategy for clinical cancer biomarker detection. The proposed platform holds great promise for point-of-care diagnostics and opens new avenues for the development of next-generation electrochemical immunosensors.