Determination of ethephon residues in fruits using fluorescent covalent organic framework-based nanomaterials

Ethephon (ETH), is an important phytohormone used as a pesticide in agriculture, the overuse of which has caused numerous health problems due to its toxicity. There is an urgent requirement to establish a testing platform that is convenient, accurate, and sensitive in detecting ETH. Herein, we devised an imine groups-based covalent organic framework (COF) with methoxy group as a fluorescent probe for ETH detection. This COF contained a rich imine structure which facilitated acids-responsive characteristics, leading to increased fluorescence response when protonated. Upon exposure to ETH, there was a notable increase at 510 nm, triggering a color transition in fluorescence from yellow to green. This change in fluorescence intensity was directly correlated with ETH concentrations ranging from 0.1 mg/L to 400 mg/L, with a limitation of detection as low as 0.05 mg/L. The practicality was demonstrated through the detection of ETH in strawberries, pepino melon, and persimmons, showing its potential for broad application in ETH analysis.