A simple yet effective colorimetric assay for nitrite based on nitration of a near-infrared (NIR) absorbing dye IR780

Nitrite (NO2-) is a unique active ion involved in the nitrogen biochemical cycle which is very important to life on earth. Besides, it is indispensable additive to preserve nutrients in diverse food products. However, the concentrations above allowable limits pose considerable threat to human health and require urgent attention. In this study, we report a novel detection strategy by using IR780 dye as a near-infrared (NIR) probe which shows unexpected colorimetric response to NO2- ions with excellent selectivity, a rapid response (<5 s) and a low detection limit (227 nM). The probe produces the distinct color change from chartreuse to violet with a 220 nm of large hypsochromic (blue) shift caused by the nitration of IR780 in the presence of NO2- ions. Smartphone-based imaging has been further employed for real time and on-site visual detection of NO2- ions which will widen the application area of our system in environmental safety and food quality. In addition, the probe IR780 has shown excellent sensing performance in complex environments such as tap water and processed meat products with high recovery rates (85-113 %) and reproducibility (RSD < 5 %). Overall, the results demonstrate that the new system is capable of sensing NO2- ions in water resources as well as complex food matrices with high sensitivity and selectivity.