Harnessing intrinsic electron-blocking effect of wide-bandgap BiCoO₃ nanosheets for ultrasensitive label-free impedimetric immunodetection of carcinoembryonic antigen.

The early and accurate detection of carcinoembryonic antigen (CEA) is critical for cancer diagnosis and prognosis. Herein, we report a novel label-free electrochemical impedimetric immunosensor based on the intrinsic electron-blocking effect of wide bandgap perovskite type BiCoO₃ nanosheets (BiCoO₃ NSs) for the ultrasensitive detection of CEA. The BiCoO₃ NSs were synthesized via a facile hydrothermal method followed by calcination, exhibiting a defined hexagonal flakelike morphology with a large specific surface area for efficient antibody immobilization. Leveraging its wide bandgap (~ 4.2 eV) and n-type semiconducting nature, the BiCoO₃ modified electrode significantly hinders interfacial electron transfer, enabling remarkable signal amplification without the need for noble metal modification. Under optimized conditions, the proposed immunosensor exhibits an ultralow detection limit of 0.01 pg mL⁻¹, a wide linear range (50 fg mL⁻¹ to 1.0 µg mL⁻¹), high sensitivity, and excellent selectivity. The sensor demonstrates satisfactory accuracy in human serum analysis with recoveries exceeding 97%, highlighting its great potential as a reliable and cost effective platform for clinical CEA monitoring and early cancer diagnostics.