Detection of live/dead Staphylococcus aureus cells based on CdSe quantum dots and propidium iodide fluorescent labeling

Abstract

A method of detecting live/dead Staphylococcus aureus cells was developed based on CdSe quantum dots-immunoglobulin G and propidium iodide fluorescent labeling. CdSe quantum dots were synthesized and surface-modified with immunoglobulin G and subsequently subjected to label S. aureus. The live S. aureus cells were stained by CdSe QDs-IgG using S. aureus protein A as target. The results showed that CdSe quantum dots with carboxyl were highly luminescent, stable, and successfully conjugated with the immunoglobulin G after staining (40 min). The optimal concentration of the immunoglobulin G coupled with CdSe quantum dots (1.0 mg/ml) was 80 ng/ml. Quantum dots-immunoglobulin G had high affinity to the surface protein A of S. aureus and exhibited high recognition property for three pathogenic S. aureus compared to Escherichia coli,Streptococcus thermophilus, and one non-pathogenic S. aureus. The fluorescence intensity of CdSe quantum dots decreased with an increasing ratio of dead S. aureus, while the fluorescence intensity of propidium iodide increased. Key words: Staphylococcus aureus, CdSe quantum dots, Staphylococcus aureusprotein A, immunoglobulin G, propidium iodide, fuorescence resonance energy transfer.