An enhanced-stability metal–organic framework of NH2-MIL-101 as an improved fluorescent and colorimetric sensor for nitrite detection based on diazotization reaction

Nitrite ion (NO2-) is a typical contaminant that can cause severe damage to the human body. Diazotization-based fluorimetric methods used for the efficient and selective detection of NO2- under a strong acidic condition remain a huge challenge. In this study, a specific nanoprobe was developed through the functionalization of the luminescent MOF of NH2-MIL-101 with Polyvinylidene fluoride/polyvinylpyrrolidone (PVDF/PVP) for detecting NO2- based on diazotization reaction. After functionalization, the resultant NH2-MIL-101 @PVDF/PVP exhibited enhanced stability even under a strong acidic condition and featured higher fluorescence intensity. Because NO2- reacted with the -NH2 group of the probe to form diazonium salt, a significant fluorescence signal was obtained. With the addition of N-(1-Naphthyl) ethylenediamine, the diazonium salt significantly changed from colorless to a purple-red color under direct sunlight. The developed dual-signal readout sensor exhibited high sensitivity, high selectivity, and good linearity in the range of 0.67–20 μM with a limit of detection of 0.67 μM. Owing to the unique properties of MOFs, the proposed sensor was characterized by simple preparation, high sensitivity, and fast response kinetics compared with the traditional sensing reagents. This study provides a potential strategy for fabricating smart fluorimetric probes used for nitrite detection.