Green synthesis of capped gold nanoparticles and their effect on Gram-positive and Gram-negative bacteria.

Aim: We report synthesis of capped gold nanoparticles (C-AuNPs) of ≈20-30 nm by reducing HAuCl4 with flower and leaf extracts of Ocimum tenuiflorum , leaves of Azadirachta indica and Mentha spicata and peel of Citrus sinensis plants.

Methods: Atomic force microscopy (AFM) and transmission electron microscopy (TEM) determined their size, shape and topographical structures. The C-AuNPs with UV-Vis spectrophotometer produced a maximum absorption within 530-535 nm wavelengths. Their Fourier transform IR stretching frequencies, from 450 to 4000 cm-1 , have inferred HAuCl4 reduction to Au.

Results: The 512 and 600 μgml-1 C-AuNP MICs were expressed on antimicrobial strains Staphylococcus aureus, Pseudomonas aeruginosa and Klebsiella pneumoniae , respectively.

Conclusion: The chosen plant extracts have reduced the Au3+ to Au0 with simultaneous in situ capping with bacteria inhibiting activities. Green routes for C-AuNP synthesis could be an asset for several other biomedical and bioengineering applications.