Gold nanorod production by cyanobacteria—a green chemistry approach

Intracellular bioconversion of auric ion (Au3+) to gold nanorod (Au0) by the cyanobacterium Nostoc ellipsosporum has been observed for the first time in laboratory condition. The nanorods were produced within the cell after exposing the healthy growing filaments to 15 mg L−1 gold (III) solution (pH 4.5) for 48 h at 20°C. The gold nanoparticles were extracted with sodium citrate solution and were subjected to UV–Visible spectroscopy. The characteristic surface-multiple plasmon bands at 560, 610, and 670 nm were observed. The nature and size of the particles were determined by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), and zeta potential studies. The nanorod size ranged from 137 to 209 nm in length and 33 to 69 nm in diameter. DLS study revealed the average hydrodynamic size as 435 nm and XRD study indicated the reduction of Au3+ to Au0. Methods of extraction and preservation of gold nanorod particles have also been studied.