Extracellular biosynthesis of platinum nanoparticles (PtNPs) using microorganisms due to its easiness of extraction has got more attention. The aim of this study was to compare application of supernatant and cell-free extract of B. safensis MN18 for biosynthesis of PtNPs. Bacterium MN18 was cultured in LB Broth medium and the cell pellet and supernatant were separated by centrifugation. For PtNPs biosynthesis, supernatant and cell extract mixed with solution H2ptcl6 (0.01M) at a ratio of 2: 1 then incubated for 168 hours and 1 hour, respectively. Characteristics of PtNPs were investigated by spectrophotometry (UV-vis), XRD, FTIR, and DLS analysis. Color changed from yellow to golden brown in solution containing bacterial supernatant while a yellow-brown liquid colloid observed in solution inoculated with MN18 cell-free extract. That can be considered prior approval for the synthesis of platinum nanoparticles. Absorption spectra of cell extracts and supernatant were recorded in 331 nm and 264 nm, respectively. Dynamic light scattering of cell extracts and supernatant showed particles size between63/67- 75/97 nm and 14/85- 75/97 nm, respectively. Also X-ray diffraction results showed 111, 200 and 220 planes of platinum cubic nanocrystals for two samples. The results of this research suggest that cell-free extract method is suitable option for production of PtNPs because of larger scale yields and better quality.

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