Luminescent Cu nanoclusters-encapsulated ZIF-8 as on-off-on fluorescent probe for efficient and selective quantification of E. coli

Abstract

Rapid and accurate detection of Escherichia coli (E. coli) is critical for maintaining water quality, and protecting aquatic ecosystems and public health. This research focuses on the development of a Förster resonance energy transfer (FRET)-based "turn-on" fluorescent nanosensor for real time, sensitive detection of E. coli. Copper nanoclusters-encapsulated metal organic frameworks (CuNCs@ZIF-8) were sythesized as a fluorescent donor with excellent luminescence properties. Further, MnO₂ nanospheres were synthesized as a receptor with good adsorption and quenching abilities. This novel nanoconjugate (CuNCs@ZIF-8@ MnO₂) was employed for the construction of a sensitive, accurate, and rapid sensing platform against E. coli in water on the basis of p-benzoquinone/hydroquinone (p-BQ/HQ) redox pair formation. Fluorescence is quenched by energy transfer when MnO₂ nanospheres are added to CuNCs@ZIF-8. Upon contact with E. coli, NADH-quinone reductase converts p-BQ to HQ, which reduces MnO₂ to Mn²⁺, releasing the nanospheres and restoring fluorescence in the composite. Based on this FRET ON-OFF-ON fluorescent probe, E. coli can be detected across a broad concentration range (5 × 10¹ to 5 × 10⁵ CFU/mL), with a detection limit as low as 8 CFU/mL within 50 min. The sensor's practicality was verified through the investigation of E. coli in real water samples, with recoveries in the range 94.3 to 106.5%. This approach offers an efficient method for on-site detection and quantification of E. coli in both environment and food safety domains.

Keywords: E. coli; Biosensors; Förster resonance energy transfer (FRET); Luminescence; Metal organic frameworks (MOFs); Water quality analysis.