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

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.