The unusual and novel properties of metal nanoparticles are highly sought after in a number of new and existing industries. Current chemical methods of nanoparticle synthesis have shown limited success and it is expected that the use of a biological approach may overcome many of these obstacles. The exploitation of microorganisms for the biosynthesis of metal nanoparticles is an area of research that has received increasing interest over the last decade. The use of living microbes as a tool for nanoparticle biosynthesis has been researched extensively, however the use of the cellular extract within the cells, excluding the living organism as a whole, has not received much attention. In this investigation, the cell-free, cell-soluble protein extract from a consortium of sulfate-reducing bacteria was used successfully in the biosynthesis of geometric Pt(0) nanoparticles, where previously, whole cells from the same culture had only resulted in amorphous Pt(0) deposits. It appears that by removing the spatial restrictions imposed by the cell itself, nanoparticles could form. It was also found that by altering the ratio of Pt(IV) to protein concentration in solution, a variety of particle morphologies resulted. (C) 2010 Elsevier Inc. All rights reserved.