Ultrasensitive Electrochemical Biosensor Based on Efficient PDA-APDMAO Antifouling Interface and Dual-Signal Ratio Strategy for Trace Detection of Alpha-Fetoprotein in Human Serum

In electrochemical analysis, developing biosensors that can resist the nonspecific adsorption of interfering biomolecules in human serum remains a huge challenge, which depends on the design of efficient antifouling materials. Herein, 3-aminopropyldimethylamine oxide (APDMAO) biomimetic zwitterions were prepared as antifouling interfaces. Among them, the unique positive and negative charges (N+–O–) of APDMAO promoted its hydrogen bonding with water molecules, forming a firm hydration barrier that endowed it with strong and stable antifouling performance. Meanwhile, its inherent amino groups could copolymerize with the biomimetic adhesive dopamine to form a thin layer of quinone intermediates, providing conditions for the subsequent binding of aptamers and signal probes. Importantly, the biomimetic APDMAO with functional groups and one-step oxidation characteristics solved the challenges of zwitterionic synthesis and modification, as well as improved biocompatibility of the sensing interface, thereby expanding the application potential of zwitterions as antifouling materials in sensing analysis. Thiol-containing alpha-fetoprotein (AFP) aptamers modified with methylene blue (MB) were coupled under controllable potential, greatly reducing the incubation time, which promoted the productization application of biosensors. In addition, the ratio sensing strategy using MB as internal standard factors and concanavalin-silver nanoparticles (ConA-Ag NPs) as signal probes was introduced to reduce background and instrument interferences, thus improving detection accuracy. On this basis, the proposed antifouling electrochemical biosensor achieved sensitive and accurate AFP detection over a wide dynamic range (10 fg/mL–10 ng/mL), with a low detection limit of 3.41 fg/mL (3σ/m). This work provides positive insights into the development of zwitterionic antifouling materials and clinical detection of liver cancer markers in human serum.