Green synthesis of silver-coated zinc oxide nanocomposite using the walnut green husk extract and assessment of its cytotoxicity and antimicrobial activity against Streptococcus mutans

Nematollahi, Hossein; Movahhed, Taraneh; Darroudi, Majid; Rakhshandeh, Hasan; Farsiani, Hadi; Charmeh, Alieh

doi:10.22038/ajp.2026.27391

Green synthesis of silver-coated zinc oxide nanocomposite using the walnut green husk extract and assessment of its cytotoxicity and antimicrobial activity against Streptococcus mutans

Document Type : Original Research Article

Authors

Hossein Nematollahi ¹

Taraneh Movahhed ¹

Majid Darroudi ²

Hasan Rakhshandeh ³

Hadi Farsiani ⁴

Alieh Charmeh ¹

¹ Department of Pediatric Dentistry, School of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran

² Department of Modern Science and Technology, Mashhad University of Medical Sciences, Mashhad, Iran

³ Department of Pharmacology, Pharmacological Research Center of Medicinal Plants, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran

⁴ Department of Microbiology and Virology, Antimicrobial Resistance Research Center, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran

10.22038/ajp.2026.27391

Abstract

Objective: This study aimed to synthesize and characterize silver-coated zinc-oxide (ZnO/Ag) nanocomposite using green husk extract of Persian Walnut (Juglans regia L.) and evaluate its cytotoxicity and antimicrobial activity against Streptococcus mutans.
Materials and Methods: In this in vitro experimental study, five groups were tested: hydroethanolic green husk extract (group A), green-synthesized ZnO/Ag nanocomposite using the extract (group B), chemically synthesized ZnO/Ag nanocomposite (group C), 0.2% chlorhexidine (positive control), and distilled water (negative control). Antibacterial activity against S. mutans was assessed via agar-well diffusion (inhibition zone diameters) and broth microdilution (MIC and MBC). Cytotoxicity was evaluated using the MTT assay. Tests were performed in triplicate across serial dilutions, with data analyzed by ANOVA.
Results: Group A exhibited no inhibitory or bactericidal effect on S. mutans. Group B inhibited growth at 125 ppm, and group C at 31.25 ppm. Both groups B and C reduced S. mutans colony counts by approximately 3 logs (significant vs. group A) and showed minimal cytotoxicity.
Conclusion: Both green-synthesized and chemically synthesized ZnO/Ag nanocomposites displayed lower antibacterial activity than chlorhexidine (CHX) against S. mutans, along with lower cytotoxicity, yet achieved a significant reduction in bacterial colony count.

Keywords

Dental caries

Streptococcus mutans

Zinc oxide

Nanocomposites

Green synthesis

Green husk

Subjects