Ultrasensitive Electrochemical Detection of Alpha–Fetoprotein Using an Aptamer–Functionalized Graphene–Gold Nanocomposite for Early Hepatocellular Carcinoma Screening

Early detection of hepatocellular carcinoma remains challenging, as clinically meaningful biomarker levels are often extremely low and conventional serological methods still suffer from insufficient sensitivity and specificity. In this work, a label-free electrochemical aptasensor for alpha-fetoprotein was developed using a graphene–gold nanocomposite directly formed on a glassy carbon electrode through one-step electrochemical co-deposition. During 20 cyclic-voltammetry deposition cycles, reduced graphene oxide and gold nanoparticles were generated simultaneously, yielding a rough, highly conductive interface with evenly dispersed nanodomains and a mean particle size of 25 ± 4 nm. The surface roughness reached 18.6 nm, over 20 times greater than that of the unmodified electrode, which favored efficient immobilization of the thiolated AFP aptamer via Au–S bonding. The staged interfacial construction was confirmed by cyclic voltammetry and electrochemical impedance spectroscopy: charge-transfer resistance dropped from 152 Ω for the bare electrode to 38 Ω after nanocomposite formation, then rose to 1180 Ω after AFP binding. Under optimized conditions, differential pulse voltammetry produced a linear response over 0.1 pg mL⁻¹–100 ng mL⁻¹, with R² = 0.998 and a detection limit of 0.03 pg mL⁻¹ calculated by the 3σ/S method. Triplicate calibration data showed small error bars, while the platform also exhibited good selectivity, a 3.8% inter-electrode relative standard deviation, 92.5% signal retention after 30 days at 4 °C, and recoveries of 97.8%-104.2% in diluted serum. These results demonstrate a simple and robust nanostructured interface for ultrasensitive AFP analysis and highlight its promise for early HCC screening.