Gummy gold and silver nanoparticles of apricot (Prunus armeniaca) confer high stability and biological activity

Abstract

Gold and silver nanoparticles (Au- and Ag-NPs) were biosynthesized using the gum extract of Prunus armeniaca. These were characterized with UV–Vis spectroscopy, FTIR, SEM, EDX, XRD and atomic absorption (AA). The effect of gum and metal ions concentration, reaction temperature and time on the synthetic stability of nanoparticles was studied along with their post-synthetic stability against varying pH and salt concentrations, long term storage and extreme of temperature. Au- and Ag-NPs were also tested for antibacterial, antinociceptive and anti-inflammatory activities. Formation of Au- and Ag-NPs was confirmed from the surface plasmon resonance centered at 555 and 450 nm respectively and was further corroborated from the results of FTIR, EDX, XRD and AA. SEM analysis showed that Au- and Ag-NPs were mostly spherical and in the size range of 5–40 nm. It was observed that 0.5% w/v gum, 3 mM Au/Ag ions solution, reaction temperature of 80 °C and reaction time of 4 h were suitable for the efficient synthesis of Au- and Ag-NPs. The results of post-synthetic stability revealed that Au- and Ag-NPs were stable in different concentrations of NaCl (1–3 M), neutral to acidic pH (7–2) and without any long term storage (eight months) or thermal (100 °C) induced degradable changes. The TGA spectrum further confirmed their thermal stability, where three successive weight losses were observed in the temperature range of 50–800 °C. Au- and Ag-NPs possessed mild to moderate antibacterial activity as observed from their zone of inhibition against Staphylococcus aureus (10 ± 0.3 mm, 18 ± 0.5 mm), Escherichia coli (9 ± 0.5 mm, 10.2 ± 0.8 mm) and Pseudomonas aeruginosa (7.9 ± 0.3 mm, 11.2 ± 0.3 mm). Au-NPs significantly alleviated the acetic acid induced writhes at much lower doses of 40 mg/kg (P < 0.01) and 80 mg/kg (P < 0.001) compared to that of gum extract at 200 and 400 mg/kg (P < 0.001). At similar doses, Au-NPs also significantly inhibited the carrageenan induced paw edema during the 1st h (P < 0.05) and 2–5 h (P < 0.001) of the study duration.