Zein and Lignin-Based Nanoparticles as Delivery Systems: Pesticide Release and Nanoparticle Health Impact on Soybeans
Abstract
It is critical to understand the impact of polymeric NPs on plants if these particles are to be used as agrochemical delivery systems. The majority of published research on the effect of engineered nanoparticles on terrestrial plant species is focused on inorganic nanoparticles, with the effects of organic polymeric nanoparticles (NP) on plants remaining largely unexplored. This study investigates the effect of biodegradable polymeric lignin-based nanoparticles (LNPs) and zein nanoparticles (ZNP) on soybean plant health. The LNPs were synthesized by emulsion evaporation from lignin-graft-poly(lactic-co-glycolic) acid, and ZNPs were synthesized by nanoprecipitation. Dynamic light scattering confirmed that LNPs measured 114 ± 3.4 nm in diameter, with a narrow size distribution and a zeta potential of -53.8 ± 6.9. ZNPs measured 142 ± 3.9 nm and had a zeta potential of +64.5 ± 4.7 mV. Soybeans were grown hydroponically and treated with 0.02, 0.2, and 2 mg/ml of LNPs or ZNPs at 28 days after germination. Plants were harvested after 1, 3, 7 and 14 days of particle exposure and analyzed for root and stem length, chlorophyll concentration, dry biomass of roots and stem, as well as total C, N, P, K, Ca, Mg, S, Fe Na, Al B, Cu, Mn, Mo, and Zn. Root and stem length, chlorophyll, and dry biomass did not differ significantly between treatments and controls for LNPs-treated plants at all concentrations, and at low doses of ZNPs. At 2 mg/ml ZNPs, chlorophyll levels increased by 12%, root biomass increased by 31%, and stem length was reduced by 16% in comparison to the control. Nutrient uptake was largely unaffected by 0.02 and 0.2 mg/ml ZNPs. However, at day 7, treatment of 2 mg/ml, Na increased (by 9% in stem and leaves and 78% in roots) and an increase in Fe uptake was observed in the roots for both ZNPs (by 117%) and LNPs (by 50%). Additionally, an increase in Cu uptake (by 67%) and a reduction of Al and Mg (by 43% and 40% relative to control) was observed in the ZNPs treated soybean roots at high concentration of particles. To our knowledge this is the first study to show the effect of zein and lignin based polymeric NPs designed for agrochemical delivery on soybean plant health.
Polymeric nanoparticles have the potential to reduce the environmental impact when used as pesticide delivery systems due to their biodegradable, tunable and controlled delivery characteristics. Nanoparticles made of lignin grafted with synthetic PLGA (LN-PLGA) were developed into environmentally responsive delivery systems for controlled delivery of methoxyfenozide (MFZ). Two types of lignin, alkaline lignin (ALN) and lignosulfonate (SLN) were grafted with PLGA at different ratios (1:2 or 1:4 w/w) and the effect of the type of lignin and LGN:PLGA ratio on the release of MFZ was compared at pH 4, 7 and 11 at two temperatures, 25 and 37°C. Monodisperse nanoparticles of 85.75 ±0.90 nm, 168.1± 1.14 nm, 156.3 ± 1.93 nm and 165 ± 2.29 nm were successfully synthesized from 1:2 w/w ALN:PLGA, 1:4 w/w ALN:PLGA, 1:2 w/w SLN:PLGA and 1:4 w/w SLN:PLGA respectively, all negatively charged with a zeta potential of < -40 mV. Thermal analysis indicated that NPs had a Tg ranging between 35-46°C and a maximum thermal decomposition temperature ranging from 250-350°C depending on the type of lignin and polymer ratio. Faster release was observed at higher temperatures 37°C relative to 25°C. pH did not significantly impact MFZ release from the ALN formulations, but it did for SLN at 1:4 LGN:PLGA w/w with MFZ releasing faster under basic pHs. Release kinetics indicated that MFZ release from ALN-PLGA and SLN-PLGA followed second order kinetics with the exception of 1:2 w/w ALG-PLGA at 25 °C and SLGN-PLGA at 37°C. The lignin-based nanoparticles developed in this study are of interest for controlled-release of pesticides under specific conditions of use given their temperature and pH responsive properties.