Multifunctional halloysite nanotube–polydopamine agro-carriers for controlling bacterial soft rot disease

Abstract

Current pesticide formulations suffer from instability and susceptibility to drift, which diminish their effectiveness and harm the environment. To circumvent these challenges, we have developed a core–shell carrier by employing in situ polymerization of dopamine on halloysite nanotubes (HNTs), loaded with the antibacterial essential oil thymol. This hybrid system demonstrates a 2.5-fold higher content of loaded thymol and a 3-fold slower release rate compared to a control lacking the 10 nm thick polydopamine layer. Additionally, the polydopamine coating confers dual-stimuli responsiveness to both acidic pH (mimicking plant infection sites) and near-infrared (NIR) irradiation (mimicking natural sunlight). Consequently, the functionalized clay shows a 2.5-fold increase in inhibiting the major plant pathogen, Erwinia carotovora, at pH 5 compared to a neutral pH. A similar trend is observed under NIR irradiation, attributed to the photothermal properties of polydopamine in combination with thymol release. In terms of crop safety, our polydopamine-coated HNT-based nanocarriers are found to be non-phytotoxic to tomato plants and show no evidence of foliar uptake as confirmed by confocal microscopy. The mussel-inspired polydopamine shell also enhances thymol stability under UV irradiation, and improves the wettability and leaf adhesion of the formulation, thereby reducing drift under simulated rainy conditions. Ultimately, the designed hybrid material exhibits superior in planta efficacy in controlling soft rot disease in tomato crops. We believe our clay-based core–shell agro-nanocarrier loaded with thymol offers a sustainable alternative to existing pesticide formulations while providing enhanced efficacy, stability, and crop safety.