An activated methylene-based fluorescent probe for the detection of nitrite in acid-free media

Currently, the mainstream strategy for NO₂^- sensing is the use of amino group as the recognition site and Griess reaction as signaling. However, this method suffers from the shortcomings of relying on strong acidic media and being susceptible to interference from amino species. Herein，we synthesized a novel fluorescent probe (OHQ) for NO₂^-. OHQ possesses a methylene activated by cyano group, enabling it to easily react with NO₂^- in a neutral medium. With the addition of NO₂^-, the fluorescence intensity of OHQ is significantly quenched in an acetonitrile-PBS solution (10 mM, pH 7.0). From this principle, a sensitive and selective method for detecting NO₂^- was developed, which offers a good linearity ranging from 0 to 55 μM and a lower limit detection of 2.5 nM (3σ). An OHQ-loaded test paper was also fabricated and applied to monitoring NO₂^- in food samples, indicating advantages of simple preparation and rapid response compared with traditional Griess reaction-based colorimetric reagents. Furthermore, OHQ was employed for fluorescence imaging and tracking NO₂^- in living cells, showing good cytopermeability, biocompatibility and fluorescence color rendering performance. Our proposed probe breaks through the bottleneck of relying on a strong acidic medium associated with traditional probes for NO₂^-, enabling it to provide a more practical method for the detection of NO₂^- and gives good application prospect.