Amine-functionalized sulfur quantum dots as highly sensitive and specific nano-bioprobes for robust immunofluorescent...

The growing burden of Staphylococcus aureus (S. aureus) infections, especially those involving antibiotic-resistant strains necessitates the development of advanced detection technologies that are rapid, selective, and adaptable to real-world conditions. In the present work, amine-functionalized sulfur quantum dots (NH₂-SQDs) conjugated with S. aureus specific antibodies have been explored for highly sensitive and specific fluorescence detection of respective bacteria. To this end, NH₂-SQDs were synthesized using solvothermal methods followed by their conjugation with polyclonal anti-S. aureus antibodies using EDC/NHS chemistry to develop immunofluorescent conjugate probe, NH₂-SQDs-Ab. The so-formed immunofluorescent probe was characterized using different spectroscopic and microscopic techniques to establish the successful synthesis and antibody conjugation. Further, the NH₂-SQDs-Ab was investigated for the precise identification of S. aureus through targeted immunofluorescence. The results demonstrated that NH₂-SQDs-Ab probe is highly specific towards S. aureus even in complicated matrices containing other interfering bacteria. The immunosensor demonstrated a strong and proportional fluorescence response to different S. aureus concentrations, thereby, achieving a detection limit of 10 CFU/mL over a broad linear range of 5× 10¹ to 5 × 10⁴ CFU/mL, along with outstanding reproducibility (R² = 0.9975). Furthermore, the developed immunofluorescent probe also showed outstanding recoveries in real-world samples, which further validates its potential for useful applications in environmental monitoring and food safety.