A novel “signal off–triggered on” Förster resonance energy transfer biosensor for the ratiometric detection of pathogenic bacteria

Abstract

Pathogenic bacterial infections pose a greatly threat to human health. Here, a novel “signal off–triggered on” Förster resonance energy transfer (FRET) ratiometric fluorescent sensor was developed for the selective detection of Staphylococcus aureus (S. aureus). Dual-recognition units, vancomycin hydrochloride (Van) anchor and aptamer affinity, enabled this sensor to accurately recognize S. aureus from other bacteria. The spectral overlap between the absorption of gold nanoclusters (Au NCs) and the emission spectrum of Ru(bpy)32+ enabled the occurrence of “signal off–triggered on” FRET, in which Au NCs were used as the energy donor and Ru(bpy)32+ as the energy acceptor, accompanied with the fluorescence quenching of Au NCs at 450 nm (“signal off” readout mode) and the signal increase of Ru(bpy)32+ at 610 nm (“signal on” readout mode). By measuring the F450 nm/F610 nm ratio, a wide linear range of 10 to 108 CFU/mL and a low detection limit of 1.0 CFU/mL were obtained for S. aureus. Satisfactory detection results in food samples and human serum, as well as ratiometric imaging of S. aureus, demonstrated the potential applications of the sensor in the early recognition of pathogenic microorganisms.