Integration of cefradine-modified dextran-coated magnetite nanoparticles and IgG-modified time-resolved fluorescent microsphere with improved performance for ultrasensitive detection of Staphylococcus aureus in clinical samples.

An improved strategy based on dual-specificity recognition synergy for ultrasensitive detection of viable Staphylococcus aureus (S. aureus) in clinical samples is proposed. A hydrophilic cefradine-modified dextran-coated magnetic nanoparticle (CDMN) was fabricated as a recognition unit for selective capture of target S. aureus. Meanwhile, a hydrophilic IgG-modified time-resolved fluorescent microsphere (ITFM) was prepared as a labeling unit for specific labeling of target S. aureus by the specific interaction between the Fc region of IgG and protein A on the surface of S. aureus. To prove the practicability, the CDMN-linked ITFM (CDMN-ITFM) strategy was constructed for the determination of S. aureus. In short, CDMN selectively captured S. aureus from complex samples containing numerous interfering molecules, and then ITFM specifically labeled S. aureus captured by CDMN; subsequently, the CDMN-bacteria-ITFM complex was isolated and washed, followed by elution to release ITFM; finally, the fluorescence signal of ITFM in the suspension was quantitatively analyzed. ‌Intriguingly, due to the presence of numerous hydrophilic groups in CDMN and ITFM, non-specific adsorption was effectively limited during the capture and labeling of S. aureus, which further reduced background fluorescence signals and improved sensitivity. Therefore, the limit of detection (LOD) of the improved CDMN-ITFM strategy was 8 CFU mL