Biosynthesis of silver, gold and silver–gold alloy nanoparticles using Persea americana fruit peel aqueous extract for their biomedical properties

While several green biomolecules have been used to synthesize functional and biologically compatible nanoparticles, little attention has been paid to Persea americana (PA) (avocado) fruit extract as a potential reducing agent. This study used avocado fruit peel aqueous extracts to synthesize silver nanoparticles (PAAgNPs), gold nanoparticles (PAAuNPs) and bimetallic alloy nanoparticles (PAAg–AuNPs). The particles were characterized using UV–vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy, selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy and X-ray diffraction among others. The particles were assessed for their antibacterial, antifungal and antioxidant properties. The UV–vis spectroscopy showed PAgNPs, PAAuNPs and PAAg–AuNPs with surface plasmon resonance at 455.5, 538 and 540.5 nm, respectively. The significant FTIR peaks: PAAgNPs (3358 cm−1), PAAuNPs (3503 cm−1) and PAAg–AuNPs (3651 cm−1) pointed to protein as both capping and stabilizing agents for the synthesized nanoparticles. Generally, the particles were spherical, with size range of 18–80 nm for PAAgNPs, 16–71 nm for PAAuNPs and 44–55 nm for PAAg–AuNPs. The energy-dispersive X-ray spectra showed silver, gold and silver/gold as conspicuous metals in PAAgNPs, PAAuNPs and PAAg–AuNPs colloids, respectively. SAED showed ring-shaped patterns for the particles. The nanoparticles effectively inhibited growth of tested bacteria (11–94%) for PAAgNPs, (10–77%) for PAAuNPs and (20–85%) for PAAg–AuNPs. The effectiveness of the biosynthesized nanoparticles can be placed as PAAg–AuNPs > PAAgNPs > PAAuNPs. The fungal inhibition performances are 33–76%, 50–82% and 27–88% for PAAgNPs, PAAuNPs and PAAg–AuNPs, respectively, while DPPH-scavenging activities were 57.82–63.25%, 15.28–54.50% and 53.05–54.26%, which were dose dependent at the tested concentrations of 20–100 µg/ml with good antioxidant activities compared to standard BHA (41.46–84.57%) and ascorbic acid (43.56–91.10%). The bleaching inhibition assay of ABTS showed activities of 56.15–85.43% (PAAgNPs), 34.67–50.93% (PAAuNPs) and 45.31–94.01% (PAAg–AuNPs). The lower concentrations of EC50 were obtained in nanoparticles (24.45–58.33 µg/ml) compared with the standards (38.42–69.04 µg/ml), indicating that the nanoparticles could suffice as good agents in drug consignment. This study has demonstrated the potential of P. americana fruit peel aqueous extracts to synthesize AgNPs, AuNPs and Ag–AuNPs for antimicrobial and antioxidant applications. The current work, to the best of our knowledge, is the first to use avocado peel extract to synthesis nanoparticles. © 2019, Springer Nature Switzerland AG.