Detecting Bacteria with Ultralow Concentrations by Enzymatic Cascade Reaction–Amplifying Strategy

Bacteria can cause infectious diseases even at ultralow concentrations (<1 CFU/mL). It is important to rapidly identify bacterial contamination at ultralow concentrations. Herein, FITC-labeled gelatinase-sensitive nanoparticles (GNPs@FITCs) and NFM@GNP@FITCs are designed and fabricated as ultralow concentration bacteria detection platforms based on an enzymatic cascade reaction-amplifying strategy. Bacterial secretions could trigger the dissociation of GNPs@FITCs to release FITC, with gelatinase used as the model secretion. The detectable signal of ultralow concentration bacteria could be amplified effectively by the gelatinase-triggered cascade reaction. Bacterial concentration was evaluated by the change in fluorescence density. The results showed that the GNPs@FITCs and NFM@GNP@FITCs could be used for identifying bacterial contamination qualitatively, even when the bacterial contamination is lower than 1 CFU/mL. Moreover, the method has better timeliness and convenience, when compared with national standards. As solid films, NFM@GNP@FITCs have better long-term storage stability than GNPs@FITCs. The potential applications of GNPs@FITC and NFM@GNP@FITCs were proved by detecting pathogenic bacteria in food. All the results showed that the method has great potential for screening pathogenic bacterial contamination qualitatively.