Phytosynthesis of gold nanoparticles using leaf extract of Coleus amboinicus Lour

Present study reports a green chemistry approach for the biological synthesis of gold nanoparticles by using the leaf extract of Coleus amboinicus Lour. The nanoparticles were structurally characterized by UV–Vis spectroscopy, XRD, TEM and SAED analyses. Elemental and vibrational analyses were done with EDAX and FT–IR spectroscopies respectively. Bioreduction of gold ions by C. amboinicus leaf extract resulted in the synthesis of spherical, truncated triangle, triangle, hexagonal and decahedral nanoparticles. These nanoparticles showed an absorption peak at 536 nm in UV–Vis spectrum corresponding to the plasmon resonance of gold nanoparticles. The size of gold nanoparticles ranged from 4.6 to 55.1 nm. FT–IR spectrum confirmed the involvement of aromatic amines, amide (II) groups and secondary alcohols in capping and reduction of gold nanoparticles. Extracellular synthesis of gold nanoparticles is a simple, cheap and environmentally benign alternative to physical and chemical procedures.

Research highlights
► For the first time, the biosynthesis of gold nanoparticles using Coleus amboinicus L. leaf extract was described. This biosynthesis is a simple, non-toxic, efficient and green chemistry approach amenable to large-scale commercial production.
► UV–Vis absorption spectra showed the reduction of gold ions to gold nanoparticles with SPR band centered at 536 nm in 1 h.
► XRD analysis of the nanoparticles showed intense peaks corresponding to (111), (200), (220) and (311) Bragg's reflection based on the fcc structure of gold nanoparticles.
► The HR-TEM analysis revealed the formation of spherical, triangle, truncated triangle, hexagonal and decahedral morphologies with an average size of 20.5 ± 11.45 nm.
► The use of environmentally benign and renewable plant material offers enormous benefits of eco-friendliness and compatibility for biomedical and pharmaceutical applications.