Smart release nanoparticles have been established in biomedical engineering as a means to release cargoes in response to a specific trigger, such as changes in temperature, pH, or biomolecule concentrations. However, this approach has not been widely applied in sustainable agriculture. This research examined applicability of smart release technologies to agriculture and developed methods toward commercial scale manufacturing. This work targeted the plant mutualist Arbuscular Mycorrhizal (AM) fungi that supports crop plants by providing phosphorous in return for carbon. AM fungi are a keystone species found on nearly every continent and associate with > 80% of vascular plants. AM fungi improve soil structure, plant stress tolerance, and water efficiency, and enlarge host plant nutrient foraging range. Here, we designed smart release hydrogels targeting AM fungi for controlled release of phosphorous to support the AM fungi-crop plant symbiosis.

We employed alginate hydrogels crosslinked by Fe^2/3+, Ca²⁺, and Ce(III) commonly found in rock. AM fungi release chelating siderophores that provide enzymatic triggers for smart release. Nanoparticles were employed to increase sensitivity to the low siderophore concentrations in soil. As commercial applications will require ~kg scales, we employed a high throughput continuous jet mixing reactor with flash nanoprecipitation. Two jet cross flows of ionic crosslinking solution impinged on a central line containing sodium alginate in water. Particle formation is induced by rapid supersaturation leading to narrow size distribution and high encapsulation efficiency. Nanoparticles were characterized using dynamic light scattering and transmission electron microscopy (Figure 1). Triggered release was analyzed using EDTA and siderophores. These results show proof of concept of smart release nanoparticles targeting the AM fungi secretome for sustainable agriculture.

Figure 1: Alginate hydrogels synthesized using flash nanoprecipitation. Average size ~ 80 nm, polydispersity of 0.26.

Alison Bennett

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