Dual-Mode Immunosensor for Antibody Detection: Harnessing the Versatility of Antibody-Based Nanozymes across Optical and Electrochemical Platforms

In the early years of the 21st century, numerous viral infectious diseases have proliferated, prompting intensified efforts to devise more effective diagnostic methods. In response, various biosensors have emerged with the aim of overcoming the constraints of conventional diagnostic techniques. Nanomaterial-based biosensors have revolutionized conventional approaches, significantly enhancing biosensor performance and effectively tackling these challenges. A diverse array of nanoparticles and nanomaterials has been systematically synthesized, engineered, and employed to augment the functionalities of biosensors. This work capitalizes on the properties of gold–platinum bimetallic nanoclusters (NCs) embedded in the structure of an immunoglobulin (IgG) (Au/Pt NCs-IgG), unveiling a novel double strategy for the detection of antibodies that leverages both their catalytic NC scaffold and the biorecognition element. The detection mechanism revealed the unique oxidase-like properties of Au/Pt NCs-IgG. This distinctive property, in addition to previously reported peroxidase-like activity, positions Au/Pt NCs-IgG as an effective probe in both optical and electrochemical sandwich enzyme-linked immunosorbent assays, facilitating their incorporation in different sensor frameworks and their utilization across various applications. As a study case, anti-SARS-CoV-2 antibodies (anti-RBD IgG antibodies) were employed as the target analyte. A linear detection range was found between 0.5 and 100 ng/mL for optical immunosensors and 50–300 ng/mL for electrochemical immunosensors. The validation of the immunosensor in clinical samples demonstrated its promising diagnostic value. The significantly differential signal obtained between positive and negative clinical samples underscores the suitability of both sensors for point-of-care diagnostic applications.