Fast detection of Staphylococcus aureus using thiol-functionalized WS 2 quantum dots and Bi 2 O 2 Se nanosheets hybrid through a fluorescence recovery mechanism.

Ultrafast and sensitive detection of Staphylococcus aureus ( S. aureus ), a harmful Gram-positive human pathogenic bacterium, by two-dimensional layered materials continues to be a challenge. Herein, we have studied the sensing of S. aureus using a tungsten disulfide (WS 2 ) quantum dot (QD) and bismuth oxyselenide (Bi 2 O 2 Se) nanosheet (NS) hybrid through their unique optical functionalities. The WS 2 QDs of a mean diameter of 2.5 nm were synthesized by liquid exfoliation. Due to the quantum confinement and functional groups, the WS 2 QDs exhibit high fluorescence (FL) yield under UV excitation. The addition of Bi 2 O 2 Se NSs resulted in the adsorption of WS 2 QDs on their surface, resulting in quenching of the FL emission due to nonfluorescent complex formation between the WS 2 QDs and Bi 2 O 2 Se NSs. A specific sequencing single-standard DNA (ssDNA) aptamer, which identifies and explicitly binds with S. aureus , was attached to the defect sites of the WS 2 QDs for selective detection. The thiol-modified ssDNA aptamers attach covalently to the WS 2 QD defect sites, which was confirmed by Raman and X-ray photoelectron spectroscopy (XPS). The interaction of S. aureus with the aptamer functionalized WS 2 QDs weakens the van der Waals interaction between the WS 2 QDs and Bi 2 O 2 Se NSs, which results in the detachment of the WS 2 QDs from the Bi 2 O 2 Se NS surface and restores the FL intensity of the WS 2 QDs, thus allowing the efficient detection of S. aureus . Similar measurements with non-targeted bacteria show that the system is quite selective towards S. aureus . Our FL-based biosensor has a linear response in the range of 10 3 -10 7 CFU mL -1 (colony formation unit mL -1 ) with a detection limit of 580 CFU mL -1 . We have observed a fast response time of 15 minutes for sensing, which is superior to the previous reports. The proposed system was tested in human urine and can detect S. aureus in human urine samples selectively, proving its potential in real-life applications. The reported approach is versatile enough for sensing other biomolecules and metal ions by choosing suitable receptors.