Fluorescent Bioconjugate Based on Gold Nanoparticles for the Determination of Staphylococcus aureus

A practical method to determine Staphylococcus aureus using bioconjugated gold nanoparticles is reported. The protocol uses gold nanoparticles stabilized by tetramethylrhodamine isothiocyanate-labeled streptavidin followed by functionalization with biotinylated anti-S. aureus antibodies. The streptavidin-stabilized gold nanoparticles were obtained by titration and analyzed by ultraviolet–visible spectroscopy and transmission electron microscopy. The obtained fluorescent bioconjugate selectively linked to the surface of S. aureus in samples contaminated with the microorganism, as demonstrated by confocal micrographs. The biorecognition process was performed by mixing the fluorescent bioconjugate with the sample. Bacterial dilutions from 1 × 108 to 1 × 102 cell/ml of S. aureus were determined, obtaining sensitivity values of 1 × 105 cell/ml by photoluminescence and 1 × 102 cell/ml by bioimpedance. This methodology represents a useful bioanalytical approach for the determination of S. aureus.