Photo-responsive supramolecular hydrogels to enhance pesticide bioavailability through multiple structural transformations

An elaborate combination of molecular self-assembly strategies and structurally reversible hydrogels can provide a versatile toolbox to address the limitations of current pesticides. However, when hydrogels are deposited on target surfaces and transferred into non-target environments, the functionalization of hydrogels with regulatory switches to realize smart, responsive release of pesticides remains a significant challenge. Herein, a ternary mixture of C 18 -modified poly (acrylic acid), α-cyclodextrin, and 1-[ p -(phenyl-azo)benzyl]pyridinium bromide was used as an assembly building block to induce reversible phase transitions between pyraclostrobin (Pyr)-loaded gel (Gel@Pyr) and Pyr-loaded sol (Sol@Pyr) by repetitive irradiations of ultraviolet (UV) and visible light. This hydrogel system exhibited excellent stability, bioactivity, and biosafety. The protection of Gel@Pyr against UV irradiation was approximately 18 times that of NSC@Pyr, which can be attributed to the shielding effect of the supramolecular gel network. Owing to the superior affinity of Gel@Pyr for the micro/nanostructures of rice leaves, droplet rebounding was inhibited, resulting in a substantial increase surface deposition approximately 10-fold compared with that of Pyr nano-suspension concentrates. Moreover, water was employed as a trigger to initiate the in situ microencapsulation of Gel@Pyr to achieve a structural transformation, which considerably reduced the acute toxicity toward zebrafish, an aquatic organism. This study aims to pave the way for designing tailored supramolecular hydrogels with multifunctionality and sustainability for smart pesticide delivery.