Deposition and water repelling of temperature-responsive nanopesticides on leaves

Global food security demands increased agricultural productivity, and pesticides play a crucial role in achieving this. However, inefficient pesticide utilization, with only 1-25% of the active ingredient reaching target organisms, is a major challenge. This inefficiency is primarily due to the poor adhesion and deposition of pesticide droplets on crop foliage, leading to significant losses through rain wash-off, photolysis, chemical degradation, and surface runoff. Abiotic and biotic stressors further exacerbate crop yield reductions, highlighting the urgent need for improved pesticide delivery systems. Enhancing the adhesion of nanopesticides to foliage is a promising strategy to address these challenges and improve agricultural productivity and climate change resilience. Previous research has explored various nanocomposite supports and additives to enhance pesticide deposition, including carbon nanomaterials, silica nanoparticles, nanogels, and polymers. However, these methods often suffer from complex formulations, low drug-loading efficiency, poor degradation properties, or a lack of strong interactions with plant surfaces. This study hypothesizes that nanopesticides prepared using biocompatible materials can improve both deposition and water repellency, maximizing pesticide efficacy. To overcome the limitations of previous approaches, the researchers utilized flash nanoprecipitation (FNP), a rapid and efficient method for producing stable and small nanoparticles with controlled surface features. FNP involves the rapid mixing of an organic solvent phase containing the pesticide and amphiphilic polymers with an antisolvent (water), leading to instantaneous nanoparticle formation. The amphiphilic polymers provide stability and inhibit particle growth. This work aims to develop a simple and efficient method to improve pesticide deposition and adhesion to leaves, leading to better pesticide utilization and reduced environmental impact.

Numerous studies have investigated methods to improve pesticide adhesion to plant surfaces. These studies explored various nanomaterials such as graphene oxide modified with Cu₂Se nanocrystals, spiky silica hollow nanoparticles, and thermosensitive nanogels based on PNIPAM. Other approaches included the use of nanocarriers like attapulgite aggregates, phosphorylated zein, and polydopamine nanoparticles. While these methods showed some success, they often suffered from complexities in formulation, low drug-loading efficiency, poor degradation properties, or weak interactions with plant surfaces. The authors highlight the need for a more efficient and biocompatible approach to address the challenges of pesticide overuse and improve pesticide utilization.

The researchers employed flash nanoprecipitation (FNP) using a confined impinging jet mixer with dilution (CIJ-D) to prepare tebuconazole (TEB) nanopesticides. The carrier material was the temperature-responsive block copolymer poly-(2-(dimethylamino)ethylmethylacrylate)-b-poly(ε-caprolactone) (PDMAEMA-b-PCL). The size, size distribution, encapsulation efficiency (EE), and drug loading capacity (DLC) of the resulting TEB nanoparticles (NPs) were controlled by varying the copolymer concentration and flow rate. The stability of the NPs was assessed over time. Transmission electron microscopy (TEM) was used to characterize the morphology of the NPs, while zeta potential measurements assessed the surface charge. Fourier-transform infrared spectroscopy (FTIR) confirmed the successful incorporation of TEB into the NPs. The stimuli-responsive release properties of the NPs were studied under varying pH and temperature conditions. Thermogravimetric analysis (TGA) was used to determine the thermal stability of the NPs. The photostability of the NPs was evaluated under UV irradiation. The wettability and foliar affinity of the TEB NPs were assessed by measuring contact angles on tomato and wheat leaves and by determining the liquid holding capacity (LHC). The rain-fastness of the NPs was examined using a wash-off method with fluorescein isothiocyanate (FITC) labeling for visualization. Confocal laser scanning microscopy (CLSM) was employed to study the uptake and translocation of the NPs in fungi (Botrytis cinerea) and tomato plants. The antifungal activity of the TEB NPs was evaluated against B. cinerea and Fusarium graminearum using a PDA culture medium assay. Protective and curative efficacy assays were conducted on tomato leaves and wheat coleoptile. Finally, the safety of the TEB NPs was assessed by evaluating their acute toxicity to zebrafish and their cytotoxicity to BEAS-2B cells using MTT assay.

The FNP method successfully produced TEB NPs with a mean diameter of ~100 nm and a narrow size distribution. The encapsulation efficiency of TEB was high, indicating efficient drug loading. The TEB NPs exhibited superior stability compared to those prepared by a conventional thermal dynamic assembly method. The TEB NPs showed stimuli-responsive release behavior, with increased release at higher temperatures and lower pH values. The NPs demonstrated enhanced thermal and photostability compared to commercial formulations. The TEB NPs exhibited significantly improved wettability on both tomato and wheat leaves, with contact angles substantially lower than those of commercial formulations. The LHC was highest for TEB NPs, indicating better retention on leaf surfaces. The TEB NPs showed significantly higher rain-fastness than commercial formulations, maintaining a substantial percentage of coverage area even after washing. CLSM studies confirmed the uptake and translocation of the NPs in both fungi and tomato plants, with limited accumulation in tomato flesh. The TEB NPs showed significantly higher antifungal activity against B. cinerea and F. graminearum compared to commercial formulations, with lower EC50 values. The protective and curative efficacy assays demonstrated that TEB NPs were superior to commercial products in controlling both fungal pathogens. The safety assessment revealed that the TEB NPs had significantly lower acute toxicity to zebrafish and lower cytotoxicity to BEAS-2B cells compared to commercial formulations.

The results demonstrate that the FNP method offers a simple and efficient way to prepare highly effective and safe tebuconazole nanopesticides. The use of temperature-responsive polymers improves pesticide deposition, adhesion, and water repellency. The enhanced antifungal activity and reduced toxicity profiles of the TEB NPs highlight their potential for improving pesticide utilization and minimizing environmental risks. The findings address the critical need for more efficient pesticide delivery systems to enhance agricultural productivity while reducing environmental impact. This innovative approach can lead to significant advancements in sustainable agriculture by maximizing pesticide efficacy and minimizing pesticide use.

This study successfully developed a novel temperature-responsive nanopesticide formulation using flash nanoprecipitation. The resulting TEB NPs exhibited superior leaf adhesion, water repellency, and antifungal activity compared to commercial formulations, while exhibiting significantly reduced toxicity. This approach offers a promising strategy for enhancing pesticide efficiency, reducing environmental impact, and improving agricultural sustainability. Future research could focus on exploring other temperature-responsive polymers and applying this method to a wider range of pesticides and crops.

While this study demonstrates the superior performance of TEB NPs, further research is needed to evaluate their long-term efficacy and environmental fate under diverse field conditions. The study primarily focused on tomato and wheat plants, and additional research is needed to assess the efficacy and compatibility with other crops. The cost-effectiveness of large-scale production of TEB NPs should also be evaluated.