Noble-metal nanoparticles directly conjugated to globular proteins.

We report the synthesis of gold nanoparticles directly conjugated to bovine serum albumin protein by chemical reduction in aqueous solution. Transmission electron microscopy reveals that the gold nanoparticles are well dispersed with an average diameter less than 2 nm, and elemental analysis verifies the composition of the gold-protein conjugates. Infrared spectroscopy confirms that the polypeptide backbone is not cleaved during the conjugation process and that the side chain functional groups remain intact. Raman spectroscopy demonstrates that the disulfide bonds in the conjugated protein are broken and thus are available for interaction with the nanoparticle surface. This synthesis method is a new technique for directly attaching gold nanoparticles to macromolecular proteins.

Bacterial biosynthesis of cadmium sulfide nanocrystals.

Semiconductor nanocrystals, which have unique optical and electronic properties, have potential for applications in the emerging field of nanoelectronics. To produce nanocrystals cheaply and efficiently, biological methods of synthesis are being explored. We found that E. coli, when incubated with cadmium chloride and sodium sulfide, have the capacity to synthesize intracellular cadmium sulfide (CdS) nanocrystals. The nanocrystals are composed of a wurtzite crystal phase with a size distribution of 2-5 nm. Nanocrystal biosynthesis increased about 20-fold in E. coli cells grown to stationary phase compared to late logarithmic phase. Our results highlight how different genetic and physiological parameters can enhance the formation of nanocrystals within bacterial cells.