Valorization of walnut shells into bioactive lignin nanoparticles: an eco-friendly hydrothermal synthesis of Se/MgO-doped composites for antimicrobial and anticancer therapy
Nada H. Aljarba, Hayfa Habes Almutairi, Nahla Alsayd Bouqellah, Adil Abalkhail, Mohamed K. Y. SolimanAbstract
This study reports the sustainable valorization of walnut shells to synthesize lignin nanoparticles (LNPs) via a hydrothermal method, followed by doping with selenium and magnesium oxide (Se/MgO) to form a composite. The nanoparticles were characterized using ultraviolet–visible spectroscopy (UV–vis), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM–EDX). Morphological analysis indicated average sizes of 72 nm (LNPs) and 79 nm (Se/MgO-LNPs) via scanning electron microscopy, with transmission electron microscopy providing higher-resolution estimates of 33 nm and 37 nm, respectively. Bioactivity assessment demonstrated potent antimicrobial efficacy against bacteria ( Bacillus subtilis, Staphylococcus aureus, Klebsiella pneumoniae, Salmonella typhi ) and fungal ( Candida albicans, Candida tropicalis ) pathogens, with electron micrographs confirming ultrastructural damage. The antimicrobial mechanism involved significant inhibition of key metabolic enzymes, including phosphoglucose isomerase (PGI), pyruvate dehydrogenase (PDH), glucose-6-phosphate dehydrogenase (G6PDH), and nitrate reductase (NR), along with induction of protein leakage from cell membranes. Additionally, both nanoparticle types exhibited dose-dependent anti-biofilm activity against S. aureus and Escherichia coli and displayed notable antioxidant capacity in 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays. In vitro cytotoxicity evaluation revealed selective anticancer activity against MCF-7 breast cancer cells, with half-maximal inhibitory concentration (IC 50 ) values of 116.8 μg/mL (LNPs) and 71.9 μg/mL (Se/MgO-LNPs). A favorable safety profile was indicated by higher IC 50 values against normal WI-38 human lung fibroblasts (448.1 μg/mL and 255.3 μg/mL, respectively).