An Electrochemiluminescence Immunosensor for Alpha-Fetoprotein Detection Based on Self-Enhancement and Resonance Energy Transfer of Polyethylenimine-g-C3N4-Luminol and CeO2@PDA

Alpha-fetoprotein (AFP), a pivotal oncofetal glycoprotein, requires ultrasensitive detection for early hepatocellular carcinoma diagnosis. This study describes a novel self-enhanced sandwich-type electrochemiluminescence (ECL) immunosensor for the highly sensitive detection of AFP based on ECL resonance energy transfer (ECL-RET) and self-enhancement by polyethylenimine. The sensor employed functionalized graphitic polyethylenimine-graphitic carbon nitride-luminol (PEI-g-C₃N₄-luminol) composite as the ECL donor and polydopamine-coated cerium oxide (CeO₂@PDA) as the acceptor. The large surface area of g-C₃N₄ nanosheets facilitated the immobilization of luminol, and the PEI on the material surface enhanced the ECL of luminol, thereby improved the detectability of the ECL signal. The ultraviolet visible (UV–vis) absorption spectrum of CeO₂@PDA exhibits partial overlapped with the emission spectrum of PEI-g-C₃N₄-luminol, thereby promoting effective ECL-RET between the donor and acceptor. In the presence of AFP, the CeO₂@PDA-Ab₂ bound to PEI-g-C₃N₄-luminol-Ab₁, forming a sandwich structure that quenched the ECL signal of PEI-g-C₃N₄-luminol. The immunosensor demonstrates outstanding performance with a strong linear response over a concentration range of 1.0 × 10⁻¹³ ∼ 1.0 × 10⁻⁷ mg·mL⁻¹ and achieves a detection limit of 5.7 × 10⁻¹⁴ mg·mL⁻¹ (S/N = 3). Moreover, the sensor exhibits excellent selectivity and stability, highlighting its potential as a reliable tool for early AFP detection in clinical diagnostics.