Biogenic gold nanotriangles from Saccharomonospora sp., an endophytic actinomycetes of Azadirachta indica A. Juss

Microbial biofabrication is emerging as eco-friendly, simpler, and reproducible alternative to chemical synthesis of metals and semiconductor nanoparticles, allowing generation of rare geometrical forms such as nanotriangles and nanoprisms. Highly confined nanostructures like triangles/prisms are interesting class of nanoparticles due to their unique optical properties exploitable in biomedical diagnostics and biosensors. Here, we report for the first time a single-step biological protocol for the synthesis of gold nanotriangles using extract of endophytic actinomycetes Saccharomonospora sp., isolated from surface sterilized root tissues of Azadirachta indica A. Juss., when incubated with an aqueous solution of chloroaurate ions (AuCl−4/1 mM). Thin, flat occasionally prismatic gold nanotriangles were produced when aqueous chloroaurate ions reacted with the cell-free extract as well as with the biomass of endophytic Saccharomonospora. It was evidenced from sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis that proteins of 42 and 50 kD were involved in biosynthesis as well as in stabilization of the nanoparticles. The particle growth process was monitored by UV–vis spectroscopy, and the morphological characterization was carried out by transmission electron microscopy and atomic force microscopy together with X-ray powder diffractions. Although the exact mechanism for this shape-oriented synthesis is not clear so far, the possibility of achieving nanoparticle shape control in a microbial system is exciting