A nano-biosensing platform based on CuS-BSA for label-free fluorescence detection of Escherichia coli†

Bacterial contamination is a serious issue for public health and food safety. In this work, a simple and label-free fluorescence detection nanoplatform for Escherichia coli (E. coli) was established on the basis of the competitive relationship for the reduction of Cu²⁺ in CuS-BSA between E. coli and O-phenylenediamine (OPD). OPD could be directly oxidized by Cu²⁺ to produce 2,3-diaminophenazine (ox OPD) with fluorescence properties. When OPD was introduced into an aqueous solution containing CuS-BSA and E. coli, the oxidation of OPD was inhibited owing to the reduction of Cu²⁺ to Cu⁺/Cu⁰ by NADH-2 dehydrogenase in the bacterial copper homeostasis mechanism, thus decreasing the fluorescence response signal of the system. Meanwhile, our strategy exhibited a satisfactory performance with a broad linear response to E. coli ranging from 12 to 1.2 × 10⁷ CFU mL⁻¹, and the limit of detection was 9 CFU mL⁻¹. The practicability of the developed fluorescence biosensing platform in real samples was evaluated by successful determination of E. coli in drinking water and orange juice. These findings provide a new sensing strategy for analyzing other foodborne bacteria and ensuring food safety assessment.