Integration of cefradine-modified magnetic nanoparticle and vancomycin-modified time-resolved fluorescent microsphere for ultrasensitive detection of Staphylococcus aureus in milk and spinach samples

Efficient separation of Staphylococcus aureus (S. aureus) from complex samples is crucial for sensitive detection. Herein, we fabricated a novel cefradine-modified magnetic nanoparticle (CMN) for selective capture of S. aureus. The biomolecule-free CMN could specifically capture target S. aureus due to the specific recognition between cefradine and penicillin binding proteins on the surface of S. aureus, and had the advantages of good stability, fast magnetic responsiveness, simple preparation, and low cost. Additionally, a new vancomycin-modified time-resolved fluorescent microsphere (VTFM) was prepared for electively labeling S. aureus captured by CMN. The antibody-free VTFM could selectively label S. aureus by the specific interaction between vancomycin and peptidoglycan on the surface of S. aureus, and could generate stable, sensitive, and easily quantifiable fluorescence signals. For proving the practicability, CMN linked VTFM (CMN-VTFM) strategy was proposed for the determination of S. aureus. Briefly, the CMN first selectively captured S. aureus from complex samples, and then the VTFM specifically labeled S. aureus captured by CMN; subsequently, CMN-bacteria-VTFM was separated and eluted to release the VTFM; finally, after removing CMN-bacteria, the VTFM was quantitatively analyzed. The biomolecule-free CMN-VTFM strategy with limit of detection of 92 CFU mL⁻¹ for milk and 73 CFU mL⁻¹ for spinach, was successfully used for detecting S. aureus in spiked real samples with recovery between 93.7 % and 100.1 % and relative standard deviation between 3.1 % and 6.1 %, respectively. Therefore, we believe that the CMN-VTFM strategy based on the antibiotic-based recognition has great potential in the field of ultrasensitive determination of pathogens.