(183k) Influence of Surface Parameters and Encapsulant Type on Nano-Pesticide Adsorption Thermodynamics on Plant Cuticle

Foliar application of pesticides is a widespread practice due to the rapid uptake of active ingredients by leaves through stomata, leaf cuticles, and trichomes, and the absorbed compounds are transported to other plant tissues via the symplast and apoplast pathways. Nano-pesticides represent the most effective form of pesticides for foliar administration, as they enhance solubility in the aqueous phase, improve bioavailability, and achieve sustained release of active ingredients. To optimize the efficacy of nano pesticides and enhance their adhesion to the plant cuticle and epicuticular waxes during spraying, it is crucial to comprehensively investigate the structural, surface, and rheological parameters that influence the thermodynamics of their adhesion.

To investigate the impact of hydrophobic, electrostatic, hydrogen bonding, steric stabilization, and Lewis’s acid-base interactive forces on the stability of the nano-pesticides and adsorption of nano-pesticides on epicuticular waxes, various nanocarriers were utilized including pluronic F-127, a triblock copolymer encapsulant; whey protein isolate, a natural protein encapsulant; Tween 80, a non-ionic surfactant; ethyl lauroyl arginate, a cationic surfactant; sodium dodecyl sulfate, an anionic surfactant; and Cocamidopropyl betaine, a zwitterionic surfactant. The nanopesticide systems were designed to maintain consistent concentrations of the active ingredient and uniform particle sizes, allowing for a focused examination of the effect of interactive forces.

Further, to elucidate the influence of surface roughness on nanopesticide adhesion, the findings from adsorption studies conducted on the adaxial side of leaf surfaces were compared with those obtained from studies on substrates coated with waxes mimicking the composition of epicuticular wax found on leaf surfaces, but lacking surface roughness.

The nano-pesticide systems, substrates, and their interactions were characterized using dynamic light scattering (DLS), scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle analysis, UV-visible spectroscopy, and fluorescence microscopy. Additionally, the kinetics of adsorption and the fate of the nano-pesticides on the wax substrates were demonstrated by monitoring changes in the frequency (∆f) and dissipation (∆D) of substrate vibrations using quartz crystal microbalance with dissipation (QCM-D), which signifies the type of nanopesticide and substrate interactions.

Based on the results, we concluded that electrostatic forces of interaction and steric repulsion between the nanopesticide system and the substrate, along with topographic roughness, are the most dominant factors influencing the adsorption of nanopesticides on the leaf cuticle and wax.