Hydrophobic CuS nanoparticle entrapment and release from lignin-derived nanoparticles

Abstract Food insecurity and environmental concerns call for increasing efficiency and sustainability of current agricultural practices. Copper-based agrochemicals, widely used to protect crops from diseases, pose risks to non-target microorganisms and groundwater due to their uncontrolled application. This study addresses these challenges by developing a controlled delivery system for Cu-based agrochemicals, enhancing their efficacy and minimizing environmental impact in agricultural applications. We investigated the synthesis of CuS nanoparticles (NPs), followed by surface modification and entrapment of hydrophobic CuS NPs in engineered lignin NPs. CuS NPs exhibited a size between 8.8±1.3 and 14.7±3.3 nm, depending on the duration of the reaction, 15 to 30 min, respectively. Surface modification of CuS NPs with 1-octadecanethiol (ODT), a thiol with 18 carbons (R-SH), resulted in hydrophobic CuS NPs. FTIR revealed a layered assembly due to arranged alkyl chains on the CuS surface. Separately, two types of lignin, alkali (ALN) and sodium ligninsulfonate (SLN), were grafted with poly(lactic-co-glycolic) acid (PLGA) at 1:1 and 2:1 w/w ratios to form amphiphilic polymers, which were assembled into delivery systems for the CuS NPs. Hydrophobic CuS were successfully entrapped into LN-PLGA delivery systems to control the release of CuS under aqueous solutions. SLN-PLGA NPs were generally smaller (122 to 130 nm) compared to ALN-PLGA NPs (132–162 nm). Release of Cu and S from the ALN-PLGA delivery systems exhibited a consistent release of S at 0.49 ppm (0.6%) for 7 days while a slow dissolution of Cu of 0.02 ppm (0.02%) was observed over the same time frame. In conclusion, CuS NPs were successfully synthesized and modified, allowing their entrapment into LNP delivery systems with different properties, and controlled release over time. The lignin-based delivery systems are proposed as feasible alternatives for the efficient delivery of CuS in nanoform, utilizing an abundant biodegradable resource for improving plant health.