Silver-Zinc oxide nanocomposite decorated cellulose nanocrystals for growth inhibition of waterborne pathogens Samudrika Aththanayake 1,2 , Gobika Thiripuranathar 2 , Sagarika Ekanayake 1 1 Department of Biochemistry, Faculty of Medicine, University of Sri Jayewardenepra, Gangodavila, Nugegoda, Sri Lanka. 2 College of Chemical Sciences, Institute of Chemistry Ceylon, Sri Lanka. Waterborne pathogen-related diseases have emerged as a major global health threat. Due to the increasing contamination of water bodies through waterborne pathogens, the current study focused on the biosynthesis of Ag-ZnO nanocomposites (NCs) integrated with cellulose nanocrystals (CNCs) derived from agro-waste of Murusi pineapple variety and studying their potential in inhibiting the growth of waterborne pathogens. Chemical pretreatment was used to isolate and produce CNCs from Murusi leaf fibers, and the CNCs were produced using a high-shear homogenization procedure. Murusi peel-mediated Ag-ZnO NCs were synthesized under various optimal conditions. Identified optimal conditions were used for synthesizing NCs, and UV-Vis, FT-IR, SEM, TEM, and XRD analyses were used to characterize the Ag-ZnO NCs. For the synthesis of Ag-ZnO/CNCs composite, CNCs (5 g) were used as the matrix phase with Ag-ZnO NCs (10 mg). The Ag-ZnO/CNCs composite ([Ag-ZnO NCs:1000 ppm]:100 µL) was tested for their antibacterial efficacy against Salmonella typhi and Shigella sonnei with positive control (Azithromycin,2000 ppm;100 µL), CNCs (100 µL) and Ag-ZnO NCs (1000 ppm:100 µL). FT- IR analysis showed no change in chemical structure following acid hydrolysis of CNCs and confirmed isolation of pure CNCs. The formation of Ag-ZnO NCs was identified through surface plasmon resonance peaks ranging from 350-475 nm. SEM analysis revealed spherical-shaped AgNPs aggregated on ZnO surface confirming the synthesis of Ag-ZnO NCs. TEM revealed the particle size of Ag-ZnO NCs ranged from 20 to 100 nm and XRD analysis demonstrated high crystallinity with hexagonal wurtzite structure and face-cantered structure that attributed to pure ZnO NPs and AgNPs, respectively. Ag-ZnO/CNCs composite exhibited antibacterial efficacy against waterborne pathogens compared to CNCs alone, which did not demonstrate any growth inhibition. Inhibition zones for Ag-ZnO NCs against Salmonella typhi and Shigella sonnei were 15±1.0 mm and 21±2.5 mm, respectively, and for Ag-ZnO/CNCs 14±1.5 mm and 19±2.0 mm, respectively. Inhibition was not significantly different (p≥0.05) between Ag-ZnO NCs and the Ag-ZnO/CNCs composite against waterborne pathogens. The study highlighted the eco-friendly applications of Ag-ZnO/CNCs for suppressing the growth of waterborne pathogens in wastewater. References 1. Sirelkhatim et al. , “Review on Zinc Oxide Nanoparticles: Antibacterial Activity and Toxicity Mechanism,” Nano-Micro Lett. , vol. 7, no. 3, pp. 219–242, Jul. 2015, doi: 10.1007/s40820-015-0040-x. 2. Parmar, S., Kaur, H., Singh, J., Matharu, A.S., Ramakrishna, S. and Bechelany, M. (2022). Recent advances in green synthesis of Ag NPs for extenuating antimicrobial resistance. Nanomaterials , 12 (7), p.1115. doi: 10.3390/nano12071115. 3. Khan, M., Karuppiah, P., Alkhathlan, H.Z., Kuniyil, M., Khan, M., Adil, S.F. and Shaik, M.R. (2022). Green Synthesis of Silver Nanoparticles Using Juniperus procera Extract: Their Characterization, and Biological Activity. Crystals , 12 (3), p.420.
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