Photoresponsive mesoporous silica nanocarriers for paraquat with substantially reduced acute toxicity and effective weed control

BACKGROUND: Paraquat (PQ) is a fast-acting non-selective herbicide, but its high mammalian toxicity and environmental risks severely limit its safe use. In this study, a photoresponsive controlled release formulation (PQ@MSN@SP) was constructed by loading paraquat into amine-functionalized mesoporous silica nanoparticles (MSN-NH₂) and using spiropyran derivatives (SP-COOH) as photoresponsive gatekeepers. RESULTS: PQ@MSN@SP nanoparticles exhibited a hexagonal prismatic morphology with an average particle size of 475.2 nm and a PQ loading capacity of 13.63%. Under UV irradiation or natural sunlight, the spiropyran moieties underwent reversible photoisomerization, which triggered PQ release. In vitro release studies demonstrated distinct photoresponsive sustained-release behavior. Stability tests further showed enhanced paraquat stability under alkaline conditions. Herbicidal assays indicated that PQ@MSN@SP maintained herbicidal efficacy comparable to that of technical-grade paraquat under sunlight exposure. Moreover, cell viability assays and acute toxicity studies in mice indicated that PQ delivery via the PQ@MSN@SP system markedly reduced cytotoxicity and acute toxicity compared with technical-grade paraquat. CONCLUSION: PQ@MSN@SP represents a safer paraquat delivery system that combines effective weed control with substantially reduced toxicity. This formulation offers a practical approach to the risk-mitigated use of highly hazardous herbicides in agricultural weed management. © 2026 Society of Chemical Industry.