Biological synthesis of gold nanoparticles by yeasts

[摘要] English: Biological systems are used to build nanoparticles of specific morphology andfunction (Eustis and EI-Sayed, 2005). The difficulty in synthesizing nanoparticlesof the desired size, shape and monodispersity directs research into new andredefined synthetic methods. The microbial interaction with metals might alsosupply eco-friendly methods for metal nanoparticle production. Various yeastspecies obtained from UNESCO MIRCEN Yeast culture collection at UFS wereevaluated for their ability to reduce Au3+ ions into elemental gold nanoparticles byvisual analysis. Colour intensity and time taken for the biomass to turn purplewere used to select for those organisms which are able to reduce gold. Theability of whole cells to reduce Au3+ ions was dependent on concentration ofgold(III) ions and (contact) time. Transmission electron microscopy (TEM)micrographs of Candida viswanathii, Geotrichum fermentans and Rodotorulagraminis showed cell bound nanoparticles. Cell free extracts of the abovementioned three species showed enhanced gold reduction over a shorter period.Physicochemical parameters such as pH, gold concentration and temperatureinfluenced the reduction and particle formation. From sub-cellular fractionation,the cytoplasm showed higher gold reduction activity. Partial purification wasachieved in two anion exchange chromatography steps and 15 fold nanoparticlegold reduction activity as well as 20 fold nitrate reductase activity. The partiallypurified fraction exhibited both nanoparticle formation and nitrate reductaseactivity. The nanoparticles formed were confirmed to be gold by EDS analysisand electron diffraction patterns were characteristic of polycrystalline material.The average size of the formed gold nanoparticles was 15 nm.

[发布机构] University of the Free State