Fluorimetric sandwich affinity assay for Staphylococcus aureus based on dual-peptide recognition on magnetic nanoparticles

A novel dual-peptide recognition strategy was designed for sandwich fluorimetric detection of Staphylococcus aureus (S. aureus) utilizing the affinity of bacterial cells for certain peptides. A phage-display peptide derived from a random peptide library was used to functionalize magnetic particles and to specifically capture S. aureus. Magainin I is a broad-spectrum antimicrobial peptide that binds to cell membranes of most bacteria. It was used as a second recognition peptide to form a sandwich complex with S. aureus. By using fluorescein isothiocyanate as the fluorescent label and working at excitation/emission wavelengths of 488/525 nm, S. aureus can be directly detected in the 10 to 10,000 cfu·mL⁻¹ concentration range, with a detection limit as low as 9 cfu·mL⁻¹. The whole detection process can be completed within 90 min. This strategy was successfully applied to the detection of S. aureus in spiked lake water, human urine and apple juice. Respective recovery values ranged from 81% to 110%. The assay is highly sensitive and specific, and fast. The use of synthetic peptides shows many advantages such as lower cost, higher stability and ease of chemical modification compared to other molecular recognition agents such as antibodies, bacteriophages, or aptamers. In our perception, this detection scheme may be extended to many other pathogens if phage-displayed peptides specific for other bacteria are available. .