Bimetallic nanoparticles synthesized from Korean red ginseng (Panax ginseng) root extract as nanocatalysts and in vitro antibacterial activity of Au-Ag alloy

Silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) were green-synthesized using Korean red ginseng root extract as a reducing agent, and both types of nanoparticles were used as seeds for the synthesis of bimetallic nanoparticles (BNPs). Five types of BNPs were synthesized by adding gold ions, platinum ions, and palladium ions to the seed colloidal solution. The synthesized BNPs were thoroughly characterized via UV‒visible spectrophotometry, field-emission transmission electron microscopy, scanning transmission electron microscopy, energy-dispersive spectroscopy with elemental mapping, high-resolution X-ray diffraction, and dynamic light scattering. The average sizes of the gold-silver BNPs (Au–Ag) (16.59 ± 5.14 nm), palladium-silver BNPs (Pd–Ag) (45.34 ± 15.14 nm), platinum-silver BNPs (Pt–Ag) (39.95 ± 9.59 nm), palladium-gold BNPs (Pd-Au) (11.09 ± 2.17 nm) and platinum-gold BNPs (Pt-Au) (12.14 ± 3.39 nm) were measured from FE-TEM images. Five types of BNPs had an alloy structure with a face-centered cubic crystallinity. In addition, Au–Ag, Pt-Au and Pd-Au were spherical, whereas Pt–Ag and Pd–Ag had sea urchin-like shapes. The atomic percentages of Pd–Ag and Pt–Ag demonstrated approximately the same ratio (50:50) of bimetals. Moreover, the spherical BNPs were composed of approximately 70% Au, and the remaining 30% consisted of Ag, Pd or Pt. Catalytic applications demonstrated that Pd-Au, with the smallest average size, had the highest catalytic activity for methyl orange (22.29 × 10^–3/sec) and Congo red degradation (12.08 × 10^–3/sec) reactions. Specifically, the highest antibacterial activity of Au–Ag at the minimum inhibitory concentration was observed against vancomycin-resistant Enterococci Van-A-type Enterococcus faecium with 9.8 μg/mL Ag and 17.3 μg/mL Au. The newly-synthesized BNPs provide nanoplatforms to explore their catalytic properties and antibacterial activity. Furthermore, the green synthesis strategy avoids the use of noxious chemicals and increases the value of Korean red ginseng root for future nanotechnology applications.