Label-Free Aptasensor Based on Functionalized Multiwalled Carbon Nanotubes for the Detection of Methicillin-Susceptible <i>Staphylococcus aureus</i>

Staphylococcus aureus is the predominant Gram-positive bacterium responsible for various infections, posing a significant challenge in clinical settings, particularly in patients with sepsis. Rapid and accurate detection of S. aureus is crucial for effective treatment, yet conventional diagnostic methods are often time-consuming procedures and lack sensitivity. This paper presents the development of a straightforward, label-free electrochemical aptasensor on an in-house-designed gold electrode for the early detection of S. aureus. The electrode is enhanced with functionalized multiwalled carbon nanotubes, significantly improving its electrochemical performance, as demonstrated by cyclic voltammetry and differential pulse voltammetry. An amino-functionalized aptamer was employed as the biorecognition element to specifically detect S. aureus, with only 2 μL of sample volume. The analytical performance of the aptasensor demonstrated a linear detection range from 101 to 106 CFU/mL of S. aureus in 1× phosphate-buffered saline, achieving a detection limit (LOD) of 2.0 CFU/mL. Remarkably, the aptasensor also achieved a low LOD of 1.34 CFU/mL in detecting S. aureus in complex matrixes such as in human ethylenediaminetetraacetic acid (EDTA)-anticoagulated whole blood without dilution, with a detection time of just 30 min. A total of 10 sepsis patients were evaluated using the developed aptasensor. The aptasensor demonstrated its strong capability to detect positive S. aureus cases, achieving a sensitivity of 100% and a specificity of 87.5%, and holds great promise for reliable detection in real clinical samples. Its rapid detection capability, simple fabrication process, and low sample volume requirements make the proposed aptasensor an affordable and practical point-of-care diagnostic tool for S. aureus infections, improving the sepsis global burden.