Green synthesis of chitosan-functionalized silver nanoparticles using non-thermal plasma as biocompatible antimicrobials against multidrug-resistant pathogens

• Green, one-step non-thermal plasma synthesis of CS-AgNPs at room temperature. • Plasma RONS enable rapid Ag + reduction and chitosan stabilization. • Monodisperse, stable CS-AgNPs with hybrid metallic/oxidized surface. • CS-AgNPs inhibit T3SS genes, reducing Salmonella virulence. • Potent, dose-dependent action against multidrug-resistant pathogens. Antimicrobial resistance (AMR) demands alternative strategies to overcome the restrictions of conventional antibiotics. This study reports the green synthesis of chitosan-functionalized silver nanoparticles (CS-AgNPs) in a one-step process at room temperature by employing a non-thermal plasma (NTP) process in an aqueous phase without using any hazardous reducing agent. Ar/H 2 plasma generated highly reactive species, thus enabling rapid Ag + reduction and simultaneously acting as a chitosan capping agent to produce crystalline, monodisperse nanoparticles. FTIR, Raman, XPS, and TEM analyses confirmed strong chitosan coordination (Ag–N, Ag–O) and uniform elemental distribution. CS-AgNPs displayed dose-dependent antibacterial activity against multidrug-resistant Escherichia coli, Salmonella enterica , and Streptococcus mutans , inhibiting their growth in the concentration range 2.34–4.69 µg/mL and reducing their colony-forming unit (CFU) count to a maximum of 1 log unit at 75 µg/mL. Cytotoxicity tests revealed that CS-AgNPs do not have any detrimental effects on RAW 264.7 and HT-29 cells at 37.5 µg/mL. CS-AgNPs inhibited the virulence genes SPI-1 and SPI-2 of Salmonella enterica, hence reducing its adhesion, invasion, and survival inside cells. These results pointed out that CS-AgNPs study in a two-step mode of action, with direct bactericidal activity and suppression of bacterial virulence, while keeping the viability of host cells intact. In conclusion, the NTP synthesized CS-AgNPs provides a biocompatible, effective, and sustainable platform to address the growing threat caused by AMR pathogens, with further applications in infection control and biomedical devices.