Smart pyraclostrobin nanopesticides based on chitosan- and pectin-gated metal–organic framework PCN-777 for boosted efficacy and biosafety

Controlled-release nanopesticides based on metal–organic frameworks (MOFs) have aroused broad interests. PCN-777, the Zr-MOF with the largest mesopores, can host the bulky broad-spectrum fungicide pyraclostrobin (Pyr). Nanoscale PCN-777 was prepared and then capped with pectin and chitosan through coordination interactions and electrostatic interactions/hydrogen bonds, respectively, to create double-gated nanofungicides. The double gatekeepers had substantial capping effect to inhibit early release of Pyr. The loading capacity of Pyr reached 25.9 % due to the large mesopores of PCN-777, higher than those in other Pyr-loaded MOF nanofungicides. The smart nanofungicides achieved the pH-, pectinase-, phosphate-, phytic acid-responsive controlled release of Pyr, which is closely associated with the physiological factors of pathogens and plants, and these stimuli-responsive mechanisms were explicitly elaborated. The nanofungicides protected Pyr from UV photolysis thanks to the shielding effect of PCN-777 organic ligands. The nanofungicides showed good fungicidal activity against fungi Fusarium graminearum (wheat head blight) and control effect of wheat powdery mildew triggered by Erysiphe graminis through foliar spray and seed coating, in comparison with commercial pesticide formulations. In terms of target plant growth biosafety, the nanofungicides improved wheat seed germination, seedling emergence, and seedling height by 10 %, 13 %, and 5 %, respectively, relative to the commercial formulation. In terms of non-target organism biosafety, the median lethal concentrations of the nanofungicides toward zebrafish were 3.6–5.7 times those of the commercial formulation, besides honeybees and human normal cells. The smart controlled-release nanofungicides have good prospective applications in the sustainable increase of agricultural products.