Biosynthesis, separation and conjugation of gold nanoparticles to doxorubicin for cellular uptake and toxicity

Particle shape and size determine the physicochemical and optoelectronic properties of nanoscale materials, including optical absorption, fluorescence, and electric and magnetic moments. It is thus desirable to be able to synthesize and separate various particle shapes and sizes. Biosynthesis using microorganisms has emerged as a more ecologically friendly, simpler, and more reproducible alternative to chemical synthesis of metal and semiconductor nanoparticles, allowing the generation of rare forms such as triangles. Here we show that the plant pathogenic fungus Helminthosporum solani, when incubated with an aqueous solution of chloroaurate ions, produces a diverse mixture of extracellular gold nanocrystals in the size range from 2-70 nm. A plurality are polydisperse spheres, but a significant number are homogeneously-sized rods, triangles, pentagons, pyramids, and stars. The particles can be separated according to their size and shape by using a sucrose density gradient using the centrifuge, a novel and facile approach to nanocrystal purification. The smallest separated gold nanoparticles were conjugated to the anti-cancer drug doxorubicin and efficient uptake by and toxicity to HEK293 cells was demonstrated.