Ultrasensitive hairpin mediated upconversion fluorescence biosensor for Staphylococcus aureus detection in foods and waters exploiting g–C3N4–assisted catalysis

A novel g-C 3 N 4 nanosheets (g-C 3 N 4 NSs)-assisted upconversion fluorescent aptasensor was proposed for Staphylococcus aureus ( S. aureus ) detection by adopting hybridization chain reaction (HCR) as a sensitizer. Two hairpin (H1 and H2) structured DNA probes were engineered predicated on the partial complementary sequence (cDNA) of S. aureus aptamer and modified on the exterior of the upconversion nanoparticles (UCNPs), respectively. The presence of S. aureus initiated the HCR system and activated H1 and H2 probes to form a double-helix away from the g-C 3 N 4 NSs vicinity. This led to the decrease in peroxidase-like activity (PA) of the g-C 3 N 4 NSs and corresponding fluorescence recovery proportional to the concentration of S. aureus (10-10 6  cfu mL −1 ). The method was applied to real food samples with acceptable recoveries (91.1–101.6%) and further validated by traditional plate counting method (p > 0.05).