Microfluidic synthesis of PLGA nanocarriers for the controlled delivery of bioactive compounds in plants of agronomic interest

Nanotechnologies are foreseen to play a crucial role in the development of new crop management techniques in the near future. In fact, nanoscale particles have properties which can allow to increase the agrochemical efficiency of pesticides, fertilizers and genetic material, delivering them in a controlled and sustained manner. Nanodelivery would significantly reduce the indiscriminate use of conventional pesticides and ensure their safe application. However, detailed knowledge of the interaction of nanosize materials with crop plants and their ultimate fate in the environment is lacking. Scientific evaluations of benefits and risks for future developments in agriculture are necessary. Such information will help the establishment of a regulatory framework for their commercialization. We developed and optimized a continuous flow microfluidic reactor that allows to precisely control some characteristics that are crucial for NPs applications as controlled size, morphology and reproducibility. PLGA-based NPs were synthesized using the solvent-displacement or nanoprecipitation technique and the effect of different fluido-dynamic conditions as well as PLGA molecular weight and concentration on NPs features (dimensions, polydispersion, morphology, stability) was studied. DLS, SEM and TEM techniques were employed to characterize the NPs. Fluorescent NPs were used to test their ability to penetrate inside plants of agronomic interest (Vitis vinifera) and some common pathogenic fungi (Botrytis cinerea, Aspergillus niger, and Aspergillus carbonarius) in fluorescence microscopy experiments, both in vitro and in vivo. Also, we entrapped in PLGA NPs some model drugs (i.e. ribavirin, methyl jasmonate, fluopyram) and studied the cytotoxicity and biochemical effects of such nanocarriers on different plant species and fungi. The optimization of the operating conditions of the microfluidic reactor allowed us to obtain spherical monodisperse NPs with controllable and tunable dimensions in the range from 25 to 300 nm [1]. By using NPs with different dimensions, we highlighted the role of the cell wall and membrane in NP size selection. We also confirmed that the uptake of PLGA NPs in plant cells follows mainly the clathrin independent endocytic pathway, without entering the lytic compartment, where they would be degraded [2]. In fact, the different bioactives loaded in PLGA NPs were able to penetrate cells, they were efficiently released and produced the expected biochemical effects, that were generally stronger, earlier and more durable than free formulations [3,4]. [1] Journal of Nanoparticle Research 2014, 16, 2703-2713. [2] Plant Cell Reports 2017, 36(12), 1917-1928. [3] Scientific reports 2019, 9, 1-9. [4] Molecules 2019, 24, 2070-2084.