<p>This study focuses on the development of a novel electrochemical biosensor for the sensitive detection of SARS-CoV-2-specific IgG antibodies. The biosensor utilizes magnetic nanocomplexes, synthesized through three distinct methods, each varying the attachment sequence of the spike protein and aminoferrocene (A-Fc) to magnetic beads. This comparative approach allowed for a thorough evaluation of the impact of preparation methods on electrochemical performance. Process 1 involved initial spike protein binding followed by A-Fc attachment, while process 2 reversed this sequence. Process 3 combined both components before attachment. These nanocomplexes were further captured IgG from the samples, and the resulting complexes were detected on anti-IgG-immobilized MWCNT-modified SPE surfaces. Electrochemical techniques, including cyclic voltammetry and differential pulse voltammetry, revealed process 2 as the most effective, demonstrating superior sensitivity and peak current responses. This outcome was supported by Raman spectroscopy and scanning electron microscopy, which highlighted the enhanced chemical modifications and surface morphology achieved through this method. Long-term stability tests showed that process 2 nanocomplexes retained over 90% of their electrochemical activity after 13&#xa0;weeks. In serum analysis, they demonstrated high recovery rates (90.83%) and low variability, outperforming processes 1 and 3. These findings establish process 2 as a reliable method for fabricating magnetic nanocomplexes, offering a robust platform for SARS-CoV-2 IgG detection and biosensing applications.</p> Graphical abstract <p></p>