A self-reportable fluorescence lighting-up nanoherbicide with minimized off-target hazards

Herbicides are the most widely used class of pesticides in modern agriculture, while they are still problematic for their off-target hazards due to volatility, drift, and leaching. Nanoformulations appear to be a promising alternative to those traditional counterparts as herbicidal delivery systems in presenting equivalent control efficacy and higher biosafety profile, but there is no approach yet to dynamically track the release of herbicidal active ingredients in weeds. To bridge the gap between the visualization of herbicidal efficacy with nanoformulation and the mechanistic understanding of the active ingredient release in vivo, we present a proof-of-concept study on the development of a green nanoformulation of herbicide (nanoherbicide) delivering 2-methyl-4-chlorophenoxyacetic acid (MCPA) based on the co-assembly of MCPA and cationic carbon dot. The release of MCPA can be tracked in vivo via a fluorescence lighting-up strategy, due to the disassembly of the nanoherbicide in weeds and the liberation of carbon dot. Compared to active ingredient, the nanoherbicide exhibits reduced volatilization rate, improved foliar affinity, and retarded leaching effect in the soil, and the hazards on off-target organisms including farming plant, soil enzymes and microbiota are appreciably minimized. Due to the characteristics of carbon dot's fluorescence quenching and lightening as the nanoherbicide forms and disassembles, respectively, the entry, translocation, and disassembly of the nanoherbicide in weeds are recorded with fluorescent microscopy. Additionally, the timing to observe the disassembly state ex vivo and to visualize the early symptoms of weed wilting match, suggesting that the released MCPA retains mechanism of action against weeds. In contrast to other labelled nanoherbicides displaying stable fluorescence, this self-reportable fluorescence lighting-up nanoherbicide provides a viable solution to predict/correlate the herbicidal efficacy with fluorescence more realistically.