An LF-NMR homogeneous sensor for highly sensitive and precise detection of E. coli based on target-triggered CuAAC click reaction.

In this study, a low field nuclear magnetic resonance (LF-NMR) homogeneous sensor was constructed for detection of Escherichia coli (E. coli) based on the copper metabolism of E. coli triggered click reaction. When live E. coli was present, a large amount of Cu²⁺ ions were transformed into Cu⁺ via copper metabolism, which then catalyzed a Cu⁺-catalyzed azide-alkyne cycloaddition (CuAAC) reaction between two materials, azide group modified gadolinium oxide nanorods (Gd₂O₃-Az) and PA-GO@Fe₃O₄ i.e., graphene oxide (GO) loaded with large amounts of alkynyl (PA) groups and Fe₃O₄ nanoparticles simultaneously. After magnetic separation, unbound Gd₂O₃-Az was dissolved by added hydrochloric acid (HCl) to generate homogeneous Gd³⁺ solution, enabling homogeneous detection of E. coli. Triple signal amplification was achieved through the CuAAC reaction induced by E. coli copper metabolism, functional nanomaterials, and HCl assisted homogeneous detection. Under the optimal experimental conditions, the linear range and limit of detection (LOD) for E. coli were 10-1.0 × 10⁷ CFU/mL and 3.5 CFU/mL, respectively, and the relative standard deviations (RSDs) were all less than 2.8 %. In addition, the sensor has satisfactory selectivity, stability and practical sample application capability, providing a new approach for the LF-NMR detection of food-borne pathogenic bacteria.