Multi-bioinspired alginate-based gel coatings formed by dynamic metal–ligand assembly for enhancing foliar affinity and rain-fastness of pesticides

Insufficient deposition of pesticide droplets and rain erosion are significant factors in excessive pesticide wastage and pose a significant threat to public health and the ecological environment. Inspired by the adhesion mechanism of marine mussels and mayfly larvae, we developed a gel coating to improve pesticide retention efficiency and resistance to rainwater washout by sequential spraying polydopamine-functionalized alginate and Fe3+ ions onto the target leaf surface (SA-DA/Fe3+). Abundant catechol groups provide strong molecular-level interfacial bridging for alginate derivates, while the gel coating contains flexible, deformable, and complex nanoscale networks, inducing mutual coupling with micro/nanostructures on the leaf surface, ultimately resulting in the removal of the interface void and the improvement of deposition capacity at multiple scales. The gel coating shows high cohesive energy to better resist rain rinsing due to the dense carboxyl-Fe3+ and catechol-Fe3+ coordination bonds in the network architecture. By combining the above effects, the pesticide retention rate of SA-DA/Fe3+ gel coating on foliage could reach about 97 % after rain erosion and immersion. In addition, the SA-DA/Fe3+ gel coating can also achieve the sensitive photo-control effect of pesticides due to the intrinsic photosensitivity of the iron-carboxylate system. Using an alginate-based gel coating as a promising strategy for improving pesticide utilization, addressing the issues of easy runoff, susceptibility to erosion, and uneven coverage in traditional pesticide droplet form, thus bridging the fields of bionic materials science, bio-macromolecular chemistry, and agricultural science.