Detecting Bacteria with Ultralow Concentrations by\nEnzymatic Cascade Reaction–Amplifying Strategy

Bacteria\ncan cause infectious diseases even at ultralow concentrations\n(<1 CFU/mL). It is important to rapidly identify bacterial contamination\nat ultralow concentrations. Herein, FITC-labeled gelatinase-sensitive\nnanoparticles (GNPs@FITCs) and NFM@GNP@FITCs are designed and fabricated\nas ultralow concentration bacteria detection platforms based on an\nenzymatic cascade reaction–amplifying strategy. Bacterial secretions\ncould trigger the dissociation of GNPs@FITCs to release FITC, with\ngelatinase used as the model secretion. The detectable signal of ultralow\nconcentration bacteria could be amplified effectively by the gelatinase-triggered\ncascade reaction. Bacterial concentration was evaluated by the change\nin fluorescence density. The results showed that the GNPs@FITCs and\nNFM@GNP@FITCs could be used for identifying bacterial contamination\nqualitatively, even when the bacterial contamination is lower than\n1 CFU/mL. Moreover, the method has better timeliness and convenience,\nwhen compared with national standards. As solid films, NFM@GNP@FITCs\nhave better long-term storage stability than GNPs@FITCs. The potential\napplications of GNPs@FITC and NFM@GNP@FITCs were proved by detecting\npathogenic bacteria in food. All the results showed that the method\nhas great potential for screening pathogenic bacterial contamination\nqualitatively.