Redox-responsive nanosilica carriers for simultaneous plant hormone release and heavy metal immobilization

Functionalized nanosilica is used to carry agrochemical IAA via disulfide bonds. • Under GSH environment, SiO 2 -S-S-IAA exhibits significant redox responsiveness. • The -SH on the surface of SiO 2 can form complexes with various heavy metal ions. • Dual-functional nanocarrier allows sustained IAA release and capture of metal ions. Owing to the low efficiency and lack of target specificity in the application of agrochemicals, e.g., plant growth regulators, the resulting environmental pollution and resource waste have raised enormous concerns over environments and human health. Herein, a redox-responsive nanosilica carrier (SiO 2 -S-S-IAA) was developed for efficient release of 3-indoleacetic acid (IAA), by functionalizing the surface of nanosilica with 3-mercaptopropyltrimethoxysilane (MPTMS), followed by the covalent coupling of IAA via redox-cleavable disulfide bonds. Under the high level of glutathione (GSH) in the plant microenvironment, IAA was released in a controlled way through disulfide bond cleavage, thus achieving redox response. In vitro controlled-release experiments confirmed that the release amount of IAA was significantly higher in the environment of 10 mM GSH, more than 10 folds at pH 5.5. Meanwhile, the thiol groups generated after release could form complexes with various heavy metal ions (Hg 2+ , As 3+ /As 5+ , Cd 2+ , Pb 2+ ), with the highest adsorption efficiency towards Hg 2 + up to 57.95%. More importantly, in planta experiments under cadmium stress have demonstrated that SiO 2 -S-S-IAA not only promoted rice seedling growth but also significantly reduced Cd 2+ accumulation in shoots, effectively inhibiting its transfer to edible parts. This work establishes a dual-functional nanocarrier platform that combines targeted agrochemical delivery with in situ heavy metal immobilization, offering a promising strategy for sustainable and precise crop protection. Download: Download high-res image (185KB) Download: Download full-size image