New formula of the green synthesised Au@Ag core@shell nanoparticles using propolis extract presented high antibacterial and anticancer activity

Abstract

Antimicrobial alternatives such as nanoparticles are critically required to tackle bacterial infections, especially with the emerging threat of antibiotic resistance. Therefore, this study aimed to biosynthesize Au-Ag nanoparticles using propolis as a natural reducing agent and investigate their antibacterial activity against antibiotic-resistant Staphylococcus sciuri (S. sciuri), Pseudomonas aeruginosa (P. aeruginosa), and Salmonella enterica Typhimurium (S. enterica), besides demonstrating their anticancer activity in cancer cell lines. The biosynthesized Au@AgNPs were characterized using UV-Vis spectrophotometer, Transmission Electron Microscopy (TEM), Zeta potential, Dynamic Light Scattering (DLS), Fourier Transformation Infrared (FTIR), and Scanning Electron Microscopy (SEM). Moreover, the detection of antibacterial activity was assessed through disc diffusion, the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC), time-killing curve, and detection of cell membrane integrity via SEM. As a result, the UV-Vis spectrum revealed the formation of Au@AgNPs in a single peak between 533 and 555 nm. Furthermore, FTIR analysis confirmed nanoparticles' green synthesis due to the presence of carbon functional groups. The formulated Au@AgNPs showed antibacterial activity against both Gram-positive and Gram-negative bacteria. The MIC and the MBC of P. aeruginosa and S. sciuri were 31.25 µg/mL. However, nanoparticles were more effective on S. enterica with MIC of 7.5 µg/mL and MBC of 15.6 µg/mL. Furthermore, the time-killing curve of the three model bacteria with the treatment was effective at 50 µg/mL. Besides, SEM of the tested bacteria indicated unintegrated bacterial cell membranes and damage caused by Au@AgNPs. Regarding the anticancer activity, the results indicated that the biosynthesized Au@AgNPs have a cytotoxic effect on HEPG2 cell lines. In conclusion, this research revealed that the green synthesized Au@AgNPs could be effective antibacterial agents against S. sciuri, P. aeruginosa, and S. enterica and anticancer agents against HEPG2.

Keywords: Antibacterial; Anticancer; Gold nanoparticles; Multi-drug resistant; Nanocomposites; Silver nanoparticles.

Fig. 1

Successive color changes during the synthesis of Au@AgNPs using ethanoic extract of propolis. AI and BI. The water is at zero point. AII and BII The water containing 3% propolis extract at zero point. AIII and BIII An intermediate step in forming the AuNPs after 80 min. AIV and BIV A late step in synthesizing the AuNPs after 120 min. AV and BV A final step in producing the Au@AgNPs, after 90 min of adding AgNO₃ to green synthesized AuNPs

Fig. 2

Various characterization techniques for Au@AgNPs. A UV–vis spectrum, B FTIR, C the zeta-potential diagram, and D DLS diagram

Fig. 3

The EDX analysis of A, B AuNPs and C, D Au@AgNPs

Fig. 4

The TEM images and suggested structures for A–D Au@AgNPs and different fields, with a scale bar of 50 nm, and E for AuNPs, with a scale bar of 100 nm

Fig. 5

The SEM images for A AuNPs and B–D for Au@AgNPs in different fields

Fig. 6

The antibacterial activity of Ag-AuNPs against the bacteria A by disc diffusion method against AI P. aeruginosa AII S. sciuri AIII S. enterica using Ag-AuNPs and the negative control for the same bacteria (AIV, AV, and AVI) respectively. Moreover, the time-killing curve during 315 min of B S. sciuri C P. aeruginosa D S. enterica after being treated with different concentrations of Ag-AuNPs. The chart E represents the readings at OD₆₀₀ after 315 min

Fig. 7

A heatmap and SEM images for the bacteria damage after adding the Au@AgNPs. The heat map of A P. aeruginosa B S. sciuri C S. enterica. The SEM images for the bacterial damage in the cell membrane of D, G P. aeruginosa, E, H S. sciuri, and F, I S. enterica after exposure to the Au@AgNPs in the concentrations marked in the black box (A–C). The orange arrows refer to the damage to the cell membrane

Fig. 8

HEPG2 cell lines after 72 h incubation with various concentrations of Au@AgNPs compared with the control (without treatment)

Fig. 9

The cell viability percentage of HPEG2 after being treated with various concentrations of Au@AgNPs (10, 20, 50, 100, 200, 500 and 1000 µg/mL). The results represent the means of three replicates, with two biological replicates and the error bars represent the standard error of the mean