On-Site Quantitative Visualization of Singlet Oxygen in Crops via an Organic Small Molecule-Based Ratiometric Fluorescent Probe and a Mobile Fluorescence Analysis Device

Singlet oxygen (¹O₂) plays imperative roles in a variety of biotic or abiotic stresses in crops. The change of its concentration within a crop is closely related to the crop growth and development. Accordingly, there is an urgent need to develop an efficient analytical method for on-site quantitative detection of ¹O₂ in crops. Here, we judiciously constructed a novel ratiometric fluorescent probe, SX-2, for the detection of ¹O₂ in crops. Upon treating with ¹O₂, probe SX-2 displayed highly selective ratiometric fluorescence response, which is favorable for the quantitative detection of ¹O₂. Concurrently, the fluorescence solution color of probe SX-2 was varied, obviously from blue to yellow, indicating that the probe is beneficial for on-site detection by the naked eye. Sensing reaction mechanism studies showed that the 2,3-diphenyl imidazole group in SX-2 could function as a new selective recognition group for ¹O₂. Probe SX-2 was utilized for the detection of photoirradiation-induced ¹O₂ and endogenous ¹O₂ in living cells. The changes in the ¹O₂ level in zebrafish were also tracked by fluorescence imaging. In addition, the production of ¹O₂ in crop leaves under a light source of different wavelengths was studied. The results demonstrated more ¹O₂ were produced under a light source of 365 nm. Furthermore, to achieve on-site quantitative detection, a mobile fluorescence analysis device has been made. Probe SX-2 and mobile fluorescence analysis device were capable of on-site quantitative detecting of ¹O₂ in crops. The method developed herein will be convenient for the on-site quantitative measurement of ¹O₂ in distinct crops.