Selective fluorescence labeling and sensitive determination of Staphylococcus aureus by microchip electrophoresis with a multiple-concentration approach

The detection of Staphylococcus aureus (S. aureus) is very important as it is responsible for bacterial infectious diseases and food poisoning. In this paper we explored the application of fluorescently labelled vancomycin to specifically bind and detect S. aureus. In view of the specificity of vancomycin towards bacterial cell surfaces, we utilized Cy5 to label vancomycin (Cy5-Van) for the identification of S. aureus. Our experiments were designed to examine in greater detail the specificity of the reaction between Cy5-Van and S. aureus. Detection parameters such as the derivatization conditions, concentrations of buffer, pH value, response performance of Cy5-Van to bacterial surface, injection time and reversed-polarity time have been investigated and optimized. To develop a simple and quick assay for the detection of S. aureus at low concentrations, we propose to use the Cy5-Van for labeling the S. aureus coupled with an on-line multiple-concentration in microchip electrophoresis. Under the optimized conditions, the detection of S. aureus was achieved within 150 s with limit of detection (S/N = 3) of 981 CFU/mL, and 350-fold enhancement was obtained for S. aureus as compared to using the no concentration step. It is self-evident that this approach has great potential in the future for the analysis of S. aureus.