Simple method for visual detection of nitrite using fluorescence and colorimetry by poly (tannic acid) nanoparticles

The nitration reaction of nitrite and phenolic substances was first used to identify and detect NO₂^- by taking fluorescent poly (tannic acid) nanoparticles (FPTA NPs) as sensing platform. With the low cost, good biodegradable and convenient water-soluble FPTA NPs, a fluorescent and colorimetric dual modes detecting assay was realized. In fluorescent mode, the linear detection range of NO₂^- was 0-36 μM, the LOD was as low as 3.03 nM, and the response time was 90 s. In colorimetric mode, the linear detection range of NO₂^- was 0-46 μM, and the LOD was as low as 27 nM. Besides, a smartphone with FPTA NPs@ agarose hydrogel formed a portable detection platform to test the fluorescent and visible color changes of FPTA NPs for NO₂^- sensing as well as for accurate visualization and quantitative detection of NO₂^- in actual water and food samples.