Enzyme-Responsive Metal–Organic Framework Nanocarrier for Carvacrol Delivery against Rice Bacterial Blight

To overcome the limited environmental stability of carvacrol (CAR) and the lack of pathogen responsive behavior in conventional delivery systems, a pectin gated metal organic framework (MOF) nanocarrier (CAR@MOF@PEC) was developed to enable stabilized and enzyme-activated delivery of CAR through a degradable polysaccharide gatekeeper. The nanoparticles had a mean hydrodynamic diameter of 256 nm and a CAR loading of 6.8%. In vitro release studies revealed that pectinase increased the cumulative release rate by about 2-fold relative to an enzyme-free control, supporting an enzyme degradable gating barrier, and baseline release was also pH-dependent. CAR@MOF@PEC inhibited Xanthomonas oryzae pv. oryzae (Xoo) with an EC50 of 4.41 mg·L–1, lower than that of technical grade CAR at an equivalent CAR dose, whereas CAR soluble concentrate (CAR@SL) showed the lowest EC50. An agar diffusion assay further confirmed clear concentration dependent inhibition zones across formulations, supporting a consistent antibacterial phenotype. Rice seed germination and early seedling growth assays indicated no detectable phytotoxicity at the tested doses. In acute aquatic toxicity assays, CAR@MOF@PEC exhibited an LC50 of 47.68 mg·L–1 in zebrafish, at least 10-fold higher than that of CAR@SL. In cell assays, CAR@MOF@PEC produced significantly greater viability than CAR@SL, with apoptosis levels close to those of the baseline. These results demonstrate an enzyme gated nanomaterial platform that integrates porous MOFs with a polysaccharide gatekeeper to enable on demand release and an improved safety profile, supporting broader use of plant derived essential oils for antimicrobial applications.