Engineered anionic and cationic lignin-g-PLGA nanoparticles for controlled delivery of nano CuS in lettuce (Lactuca sativa): effects of charge on nutrient uptake and metabolic activity

Abstract

Engineered nano-delivery systems of controlled properties have shown great potential for agricultural applications. Here, the surfactant-free synthesis of anionic lignin (aLN) and cationic lignin (cLN) nanoparticles (NPs), of controlled size and charge, was optimized and tested for the delivery of nanoscale copper sulfide (nCuS), an antimicrobial and fertilizer complex, to lettuce (Lactuca sativa). NPs were produced by sonication-driven self-assembly of an amphiphilic polymer formed by grafting native, anionic lignin, or cationized lignin with poly(lactic-co-glycolic acid) (PLGA). Core–shell NP size was controlled by varying the w/w ratio of LN : PLGA and characterized using nanoparticle tracking analysis (NTA). For anionic NPs, empty and nCuS-loaded 1 : 1 w/w aLN : PLGA averaged 111.6 (±4.1) nm, whereas 1 : 4 w/w aLN : PLGA NPs averaged 139.1 (±7.6) nm. Cationic NPs were 170.8 (±4.7) nm for 2 : 1 w/w cLN : PLGA and 172.6 (±11.0) nm for 1 : 1 w/w formulation. Zeta potentials (ζ) exceeded −70 mV for anionic NPs, and +25 mV for cationic NPs, indicating high colloidal stability. HAADF and S/TEM-EDS showed surface and cavity loading of nCuS and colocalization of Cu and S in the loaded (a/c)LNPs. Four-week-old lettuce was hydroponically exposed to (a/c)LNPs (250 mg L⁻¹) for 7 days. Inductively coupled plasma optical emission spectroscopy (ICP-OES) revealed significant Cu accumulation in roots for both aLNPs and cLNPs, while only aLNPs enabled significant Cu translocation to leaves relative to controls (5.2 ± 1.5 and 7.4 ± 3.4 versus 1.4 ± 0.4 mg kg⁻¹). High-performance liquid chromatography-diode array detection (HPLC-DAD) biomolecular profiling and protein content analysis showed no significant changes in biomolecule levels in roots and leaves, indicating minimal phytotoxicity. The successful synthesis and application of (a/c)LNPs as a delivery system for CuS is demonstrated, and the insight into the metabolic response of plants to lignin-based NP carrier systems highlights the significant promise of this strategy for future applications in sustainable agriculture.