Magnetic Nanoparticle Capture and Quantum Dot Labeling for Rapid and Quantitative Detection of Methicillin-Resistant Staphylococcus aureus

The increasing incidence of drug-resistant bacterial strains, such as methicillin-resistant (MRSA), poses a significant threat to public health owing to their high morbidity and mortality rates. Conventional methods for MRSA detection are expensive and time-consuming, necessitating advanced technological solutions. This study aimed to develop a direct detection strategy for MRSA by using magnetic nanoparticles (MNPs) as capture probes and quantum dots (QDs) as fluorescent detection probes. MNP capture probes were prepared by the coprecipitation of Fe3O4 NPs, followed by co-condensation to obtain amine-functionalized silica coatings on Fe3O4 NPs (amine-Si@MNPs). Carboxyl modification of amine-Si@MNPs was achieved via the hydrolytic cleavage of succinic anhydride. QDs were prepared using a one-pot chemical reduction method for CdTe core, followed by inorganic epitaxial growth of ZnS shell (CdTe/ZnS QDs). The size, morphology, surface functionalization, and magnetic and optical properties of the nanoprobes were characterized using several techniques. Both the nanoprobes were conjugated to protein A using carbodiimide chemistry. QD-protein A was conjugated to an anti-PBP2a antibody that specifically targets MRSA. In contrast, MNP-protein A was conjugated with human IgG to target outer membrane protein A of MRSA. MRSA detection was achieved by mixing the sample with the QD detection probe, followed by MNP capture probe, magnetic separation, and fluorescence measurements. Detection was achieved within ∼25 min, with a detection limit of 5 colony-forming units (CFU)/mL. The selectivity of this method was investigated by using mixed cultures of various bacterial isolates.