Fluorophore-free luminescent double-shelled hollow mesoporous silica nanoparticles as pesticide delivery vehicles.

Recently, mesoporous silica nanoparticles (MSNs) have become popular nanomaterials in smart delivery systems. Although research progress in the application of MSNs as pesticide carriers has been achieved, multifunctional MSNs endowed with bright luminescent centers facilitating the tracking of MSNs in biological systems and versatile structural properties possessing a high drug loading capacity and regulable release are still highly desirable. In the present work, we reported a fluorophore-free method to endow MSNs with stable fluorescence and a double-shelled hollow structure; they were prepared by a selective-etching strategy and subsequent annealing treatment. The strong and stable luminescence is found to originate from the carbon dots generated from the calcination. Their well-defined morphological structure was confirmed by SEM and TEM imaging. These versatile silica nanoparticles served as a novel delivery system for the pesticide pyraclostrobin with a loading content of 28.5%. The pyraclostrobin-loaded nanoparticles showed an initial burst, followed by subsequent sustained release behavior. The fungicidal activity of pyraclostrobin-loaded silica nanoparticles against the fungus Phomopsis asparagi (Sacc.) as well as their visual observation in the mycelium was explored. Furthermore, the effect of pyraclostrobin-loaded nanoparticles on the morphology and ultrastructure of the mycelium was investigated by SEM and TEM observations. This research seeks to develop a novel nanocarrier platform for the potential application of pesticides in sustainable plant protection.