In the present work, we studied the reduction of gold ions into gold nanoparticles using Nigella arvensis leaf extract in the one-step green synthesis method. The formation of N. arvensis gold nanoparticles (NA-GNPs) was confirmed by UV–Vis spectroscopy, XRD, FT-IR and TEM analyses. The XRD pattern confirmed the crystal structure of NA-GNPs, and TEM image showed the small size (3–37 nm) and almost spherical shape of NA-GNPs. NA-GNPs have not shown enhanced antioxidant properties compared to the plant extract while they were active against the clinical isolated bacterial strains. These nanoparticles showed the cytotoxicity effects against H1299 and MCF-7 cancer cell lines with an IC₅₀ value of 10 and 25 μg/ml, respectively. The extract of N. arvensis contained 212 μg/ml flavonoids and 145 μg/ml phenolic compounds. The contents of total phenolics and flavonoids of biosynthesized NA-GNPs were 68 and 189 μg/ml, respectively. Plant extract and NA-GNPs exhibited a maximum DPPH scavenging activity of 32% and 12%, respectively. The catalytic activity of NA-GNPs against methylene blue was 44%. In conclusion, these results suggest that NA-GNPs can act as a promising candidate for different medical applications produced by cost-effective, eco-friendly and straightforward green method.

Recently, major problem related to pathogenic bacteria is augmentation of antibiotic resistance which has been changed treatment and recovery of millions of infectious patients. The present study reports an eco-friendly, rapid and easy method for synthesis of silver (Ag), copper (Cu) and titanium dioxide (TiO₂) nanoparticles (NPs) using Artemisia haussknechtii leaf aqueous extract with antibacterial activities against multi-drug resistance (MDR) bacteria species. Three different concentrations (0.001, 0.01 and 0.1 M) of AgNO₃, CuSO₄ and TiO (OH)₂ were investigated for obtaining optimum NPs green synthesis. Total phenolic content, total flavonoid content of leaf extract and total antioxidant activity (DPPH) assay were determined as radical scavenging methods. UV–Visible spectroscopy, Fourier transform infrared spectroscopy analysis, X-ray diffraction, energy dispersive X-ray spectroscopy, field emission scanning electron microscope and atomic force microscopy (AFM) were used due to NPs characterization. The size average of the Ag, Cu and TiO₂ NPs obtained were respectively 10.69 ± 5.55, 35.36 ± 44.4 and 92.58 ± 56.98 nm. In the case of antibacterial assay, disc diffusion assay, minimum inhibitory concentration, minimum bactericidal concentration, bacterial growth and morphology of four MDR species Staphylococcus aureus ATCC 43300, Staphylococcus epidermidis ATCC 12258, Serratia marcescens ATTC13880 and Escherichia coli ATCC 25922 were evaluated. Results of this study demonstrated that A. haussknechtii leaf extract with various groups of phytochemicals such as phenols and flavonoids had suitable ability in green synthesis of Ag, Cu and TiO₂ NPs. Also, Ag and Cu NPs had more antibacterial activities compared to TiO₂ NPs.

Fighting of current antibiotics against multidrug-resistant (MDR) bacteria has not been completely successful. In this study, the bio-synthesized Ag–TiO₂, TiO₂–Ag, Ag–Cu and Cu–Ag nanocomposites (NCs) were used against MDR bacteria including Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 (gram negative) and Staphylococcus aureus ATCC 43300 (gram positive). Antiplanktonic, antibiofilm, antiswarming motility and antiquorum sensing activities of these four NCs were measured by assays of agar well diffusion, minimum inhibition/minimum bactericidal concentrations (MIC/MBC), biofilm formation, biofilm morphology and pyocyanin amounts. Agar well diffusion method illustrated higher inhibition zone diameter (IZD) of Ag-TiO₂ NCs with 13 ± 1, 16 ± 1.73 and 21.66 ± 1.52 mm against E. coli ATCC 25922, S. aureus ATCC 43300 and P. aeruginosa ATCC 27853 respectively. Swarming motility of P. aeruginosa at presence of NCs demonstrated lower density than control samples. Ordering of antibiofilm strength for these NCs was Ag–TiO₂ > TiO₂–Ag > Cu–Ag > Ag–Cu. In addition, biofilm roughness and also pyocyanin synthesis as virulence factor related to quorum sensing mechanisms of P. aeruginosa ATCC 27853 was decreased under Ag–TiO₂ NCs. In total, the present investigation illustrated eco-friendly and one-pot way to synthesize metal NCs with having significant antibacterial, antibiofilm and antiquorum sensing abilities.