Competitive Electrochemical Apta-Assay Based on cDNA–Ferrocene and MXenes for Staphylococcus aureus Surface Protein A Detection

<i>Staphylococcus aureus</i> (<i>S. aureus</i>) represents one of the most frequent worldwide causes of morbidity and mortality due to an infectious agent. It is a part of the infamous ESKAPE group, which is highly connected with increased rates of healthcare-associated infections and antimicrobial resistance. <i>S. aureus</i> can cause a large variety of diseases. Protein A (PrA) is a cell-wall-anchored protein of <i>S. aureus</i> with multiple key roles in colonization and pathogenesis and can be considered as a marker of <i>S. aureus</i>. The development of aptasensors, having an aptamer as a specific biorecognition element, increases selectivity, especially when working with complex matrices. The association with state-of-the-art materials, such as MXenes, can further improve the analytical performance. A competitive aptasensor configuration based on a ferrocene (Fc)-labeled cDNA hybridized (cDNA-Fc S13) on a specific aptamer (APT) for PrA in the presence of MXene nanosheets was designed for the indirect detection of <i>S. aureus</i>. The aptasensor displayed a linear range of 10-125 nM, an LOD of 3.33 nM, and a response time under 40 min. This configuration has been tested in real samples from volunteers diagnosed with <i>S. aureus</i> infections with satisfactory results, enabling the perspective to develop decentralized devices for the rapid detection of bacterial strains.