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 HAuCl(4) 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 HAuCl(4) 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 Au(3+) to Au(0) 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.