High-performance fluorescent and colorimetric dual-mode nitrite sensor boosted by a versatile coumarin probe equipped with diazotization-coupling reaction-sites

Nitrite has posed ubiquitous threats to the environment, human health, and public security because of its crucial role in food processing, construction, farming, and explosive manufacturing industries. To achieve accurate, sensitive, and on-site detection of trace nitrite, a colorimetric-fluorescent dual-mode sensing probe with unique photophysical process was designed for ultrasensitive determination of nitrite by precisely adjusting the amino site and significantly influencing the coupling reaction activity. This modulating strategy breaks through the dilemma of azo-product with only colorimetric phenomenon, facilitating the probe, 7-amino-4-methylcoumarin, to maintain a desirable sensitivity with detection limits of 98 nM and 629 nM in fluorescent and colorimetric modes, respectively, as well as an outstanding specificity even in the presence of 15 common anions and interfering substances. The probe was further integrated into a portable sensor by applying a polyvinyl alcohol hydrogel as a loading substrate, which showed superior sensing performances in analyzing nitrite in various real samples with visualized, anti-interferent, and dual-mode responses. Consequently, the present reaction-site modulation strategy would provide a general reference for ultrasensitive, on-site, and visual detection of nitrite, and it can be broadly applied in environmental monitoring and food safety assessment.