Hydrophilic Hairy Dual Signal-Responsive Ratiometric Fluorescent Molecularly Imprinted Polymer Microspheres for Smartphone-Assisted Visual Herbicide Detection in the Undiluted Milks

The efficient development of high-performance complex biological sample-compatible fluorescent molecularly imprinted polymers (MIPs) and their portable sensors is highly important for their real-world applications but remains challenging. Herein, we report on the efficient synthesis of hydrophilic hairy dual signal-responsive ratiometric fluorescent MIP microspheres and their smartphone-assisted highly sensitive and precise visual detection of 2,4-dichlorophenoxyacetic acid (2,4-D) in the undiluted pure milks. Core-shell-corona-structured 2,4-D-MIP particles with both green and red fluorescent species-labeling and polyethylene glycol brushes were readily synthesized via the newly developed one-pot surface-initiated activator-regenerated by electron transfer atom transfer radical polymerization (ATRP) with tris[2-(dimethylamino)ethyl]amine as both the ligand and the reducing agent for Cu(II) catalyst. This synthetic strategy could not only afford largely enhanced polymerization rate but also lead to fluorescent 2,4-D-MIP particles with obviously enhanced fluorescence responses toward 2,4-D compared with those prepared via the previously developed one-pot surface-initiated ATRP methods. Such hydrophilic dual fluorescent 2,4-D-MIP showed remarkable photostability, reusability, and long-term storage stability as well as strong 2,4-D selectivity and simultaneous large green fluorescence enhancement and red fluorescence quenching toward 2,4-D in pure milk samples, which make them promising complex biological sample-compatible chemosensors for visually detecting 2,4-D with good recoveries (98.0-104.0%) and high accuracy (≤4.0%). Notably, their obvious dual-signal responsivity imparted them with significantly enhanced optosensing sensitivity, with their limit of detection (=0.025 μM) being almost five times lower than that of our previously reported hydrophilic hairy single signal-responsive ratiometric fluorescent 2,4-D-MIPs. Finally, a smartphone-integrated portable MIP optosensor was developed for precise and selective visual 2,4-D detection in pure milks. This study opens new access for efficient development of high-performance MIP optosensors highly promising in on-site detection of complex biological samples.