Engineering a novel rhodamine-based fluorescent probe using host-guest interactions for reversible, selective, and sensitive detection of herbicide paraquat

Although paraquat (PQ) is one of the most extensively used herbicides worldwide, it is hazardous to the environment and the public due to its extreme toxicity towards non-target organisms especially animals and humans. Therefore, developing a detection system for selectively and sensitively detecting PQ remains a great challenge. This report demonstrates the design of a novel highly fluorescent rhodamine-based probe fabricated by rationally inserting adamantane-modified rhodamine into a host cucurbit[7]uril (CB[7]) with a host-guest interaction induced spirocyclic ring-opening process. This host-guest binary complex (1&CB[7]) had a stronger fluorescence intensity than rhodamine B, which was exploited for PQ detection. Notably, complex 1&CB[7] displayed high sensitivity toward PQ, with an excellent nanomolar limit of detection of 10 nM. It was determined that this unique detection mechanism involved a process of self-assembly, disassembly, and reassembly, thereby providing a reversible fluorescence response to PQ. With such merits, we successfully quantified and mapped PQ in actual water samples, live cells, and various agricultural products. We anticipated that the constructed complex 1&CB[7] could acts as a potential alternative for PQ tracking in various applications, highlighting a new paradigm for engineering host-guest probes with spirocyclic ring-opening process for analyte detection.