An efficient ratiometric fluorescence and colorimetric dual-mode probe for convenient determination of nitrite in real samples and E. coli

Developing an effective and convenient nitrite detection method is indispensable in food safety, environmental monitoring, clinical diagnosis of diseases, and many other areas. Herein, a dicyanoisophorone derivative, TMN-NH2 with large Stokes shift and near-infrared (NIR) emission, was proposed as a ratiometric fluorescence and colorimetric dual-mode probe for the rapid determination of NO2− in acidic media, showing excellent selectivity and high sensitivity. The sensing mechanism is based on the diazotization of TMN-NH2 with NO2− and subsequent diazonium salt hydrolysis to form a hydroxyl-substituted product (TMN-OH). Under the optimized conditions of reaction and detection, a new quantitative analysis method based on TMN-NH2 was established for NO2− detection, exhibiting good linear relationships to NO2− in the range of 0.5 to 15 μM with practical detection limits of 26.6 nM and 17.6 nM for the colorimetric and fluorescent readout, respectively. The quantitative detection of NO2− in real samples demonstrated satisfactory recoveries and repeatability. Moreover, TMN-NH2 was successfully applied for monitoring NO2− in Escherichia coli by confocal fluorescence imaging.