High-sensitivity electrochemical immunosensor for anti-SARS-CoV-2 IgG detection using screen-printed carbon/cerium oxide-gold electrode

Background and purpose: Serological assays are essential for evaluating immune responses, including donor screening, vaccine efficacy, and antibody persistence. However, conventional methods are time-consuming and require centralized laboratories. This study aimed to develop a sensitive and rapid electrochemical immunosensor based on a cerium oxide-gold nanocomposite (CeO₂-Au) modified screen-printed carbon electrode (SPCE) for the detection of anti-SARS-CoV-2 IgG, while elucidating the underlying electrochemical sensing mechanism. Experimental approach: CeO₂-Au nanocomposites were synthesized and characterized using UV-Vis, SEM, TEM-EDX, and FTIR. The immuno­sensor was fabricated by immobilizing SARS-CoV-2 Spike receptor-binding domain (RBD) onto the modified SPCE. Electrochemical responses were evaluated using differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) with K₃[Fe(CN)₆] as a redox probe. Key results: The CeO₂-Au nanocomposite enhanced electron transfer and provided a high surface area for biomolecule immobilization. The sensing mechanism is governed by modulation of interfacial electron transfer: binding of IgG to immobilized RBD forms an insulating immunocomplex layer, increasing charge transfer resistance and suppressing faradaic current. The sensor exhibited a wide linear range of 0.01 to 103 ng mL-1, a low detection limit of 2.475 pg mL-1, good stability, and reliable 97.3 to 108.56 % recovery in serum samples. Conclusion: This immunosensor proposed as a sensitive and reliable platform for IgG detection. The study advances understanding of signal transduction mechanisms in nanocomposite-based immunosensors and highlights their potential for rapid serological diagnostics. However, broader clinical validation and selectivity against complex interferents remain necessary.