A highly sensitive upconversion nanoparticles-WS2 nanosheet sensing platform for Escherichia coli detection

In this study, we have design a new biosensor for E. coli, based on the fluorescence resonance energy transfer (FRET) between aptamer modified upconversion nanoparticles (UCNPs) as donors and layered tungsten disulfide (WS 2 ) nanosheets as the effective acceptor. The aptamer modified-UCNPs can be fetched nearest to the WS 2 surface, because of the potent van der Waals force between the nucleobases of aptamer and the basal plane of WS 2 . The spectral overlap between UCNPs fluorescence emission and WS 2 absorption permits the occurrence of FRET, resulted in quenching of upconversion fluorescence. In the presence of E. coli , the specific aptamer preferentially bind to E. coli , causing changes in the conformation of aptamer, a phenomenon directs the dissociation of mixing probe away from the surface of WS 2 nanosheets and therefore parts of the quenched fluorescence of UCNPs was retrieved. The fluorescence intensity increased with the raised concentration of E. coli . The aptasensor exhibited limitary over the concentration range 85 to 85 × 10 7 cfu mL −1 for E. coli and the detection limit (LOD) was 17 cfu mL −1 . In addition, the proposed biosensing method comprehended huge advantages including the facile operation procedure, high sensitivity and selectivity, which confer a great potential for the quantification of E. coli in medical diagnostics, food and environmental analysis.