A pH-Responsive Essential Oil Delivery System Based on Metal–organic Framework (ZIF-8) for Preventing Fungal Disease

Smart metal–organic framework nanocarriers that respond to microenvironmental stimuli related to plant diseases can achieve the on-demand release of active ingredients to control diseases. The plant essential oil citral (CT) has significant biological activity against most pathogens but its poor stability limits its application in the field. To improve the applicability of plant essential oils, we aimed to construct a pH responsive essential oil delivery system (CT@ZIF-8) based on the zeolitic imidazolate framework-8 in this study. The high specific surface area of ZIF-8 enables CT@ZIF-8 remarkable loading capacity, and the metal–organic framework effectively delays the volatilization of CT. The results showed that CT@ZIF-8 was approximately 177 nm in size, had a stable nanostructure, and displayed a high pesticide loading efficiency (15.22%). The photodegradation rate of CT loaded in ZIF-8 under UV irradiation (48 h) was only 17.99%, much lower than that of CT alone (51.18%). The CT@ZIF-8 had a pH-responsive controlled release property, releasing CT from CT@ZIF-8 in a pH-dependent manner. The bioactivity results showed that CT@ZIF-8 had a lower EC50 than CT against three fungi (Magnaporthe oryzae, Botryosphaeria dothidea, and Fusarium oxysporum), enhancing the antifungal activity of CT. After 3 d of reagent treatment, only CT@ZIF-8 maintained good control against rice blast (75.76%) and soft rot (63.69%) infection. We have constructed a smart delivery system for essential oils, which provides a new pathway for the efficient application of plant-derived essential oils in the green control of plant diseases.