Salicylic acid (SA) is one of the chemical molecules, involved in plant growth and immunity, thereby contributing to the control of pests and pathogens, and even applied in fruit and vegetable preservation. However, only a few tools have ever been designed or executed to understand the physiological processes induced by SA or its function in plant immunity and residue detection in food. Hence, three Rh6G-based fluorogenic chemosensors were synthesized to detect phytohormone SA based on the "OFF-ON" mechanism. The probes showed high selectivity, ultrafast response time (<60 s), and nanomolar detection limit for SA. Moreover, the probe possessed outstanding profiling that can be successfully used for SA imaging of callus and plants. Furthermore, the fluorescence pattern indicated that SA could occur in the distal transport in plants. These remarkable results contribute to improving our understanding of the multiple physiological and pathological processes involved in SA for plant disease diagnosis and for the development of immune activators. In addition, SA detection in some agricultural products used probes to extend the practical application because its use is prohibited in some countries and is harmful to SA-sensitized persons. Interestingly, the as-obtained test paper displayed that SA could be imaged by ultraviolet (UV) and was directly visible to the naked eye. Given the above outcomes, these probes could be used to monitor SA in vitro and in vivo, including, but not limited to, plant biology, food residue detection, and sewage detection.
Keywords: fluorescent probe; plant imaging; residue detection; rhodamine 6G; salicylic acid.