<p>Serological testing complements nucleic acid-based assays by characterizing virus-associated humoral immune responses. However, conventional enzyme-linked immunosorbent assay (ELISA) workflows are laboratory dependent, and disposable electrochemical sensors must reconcile efficient charge transfer with stable biorecognition to support reliable serological analysis. Here, a screen-printed carbon electrode (SPCE) was modified with chitosan-functionalized nitrogen-doped graphene (N-Gr/CS) and electrodeposited gold nanoparticles (AuNPs) to construct an AuNPs/N-Gr/CS/SPCE platform for dual-mode determination of adenovirus-associated immunoglobulin G (AdV-IgG). Material and electrochemical characterization verified stepwise interface assembly and progressive enhancement of interfacial charge transfer. Scan-rate and kinetic analyses indicated adsorption-dominant redox behavior with a diffusion contribution. Under optimized conditions, the platform exhibited logarithmic concentration–response relationships in both electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). DPV achieved a linear range of 5 ng mL^-1 to 1 mg mL^-1 with a limit of detection of 3.45 ng mL^-1, whereas the corresponding EIS values were 500 ng mL^-1 to 8 mg mL^-1 and 8.01 ng mL^-1. The sensor demonstrated acceptable repeatability, inter-sensor reproducibility, and tolerance to the interferents tested. In 10-fold diluted healthy human plasma spiked with AdV-IgG, recoveries of 95.8-104.2% and agreement with ELISA at the tested spike levels supported analytical feasibility in a simplified biological matrix. Collectively, these findings establish an interfacial design strategy for dual-mode serological analysis; clinical diagnostic performance was not assessed and will require validation in adequately powered, virologically characterized cohorts of adenovirus-positive and adenovirus-negative subjects.</p>