Biosynthesis of bismuth selenide nanoparticles using chalcogen-metabolizing bacteria

Cost and energy reductions in the production process of bismuth chalcogenide (BC) semiconductor materials are essential to make thermoelectric generators comprised of BCs profitable and CO₂ neutral over their life cycle. In this study, as an eco-friendly production method, bismuth selenide (Bi₂Se₃) nanoparticles were synthesized using the following five strains of chalcogen-metabolizing bacteria: Pseudomonas stutzeri NT-I, Pseudomonas sp. RB, Stenotrophomonas maltophilia TI-1, Ochrobactrum anthropi TI-2, and O. anthropi TI-3 under aerobic conditions. All strains actively volatilized selenium (Se) by reducing selenite, possibly to organoselenides. In the growth media containing bismuth (Bi) and Se, all strains removed Bi and Se concomitantly and synthesized nanoparticles containing Bi and Se as their main components. Particles synthesized by strain NT-I had a theoretical elemental composition of Bi₂Se₃, whereas those synthesized by other strains contained a small amount of sulfur in addition to Bi and Se, making strain NT-I the best Bi₂Se₃ synthesizer among the strains used in this study. The particle sizes were 50-100 nm in diameter, which is sufficiently small for nanostructured semiconductor materials that exhibit quantum size effect. Successful synthesis of Bi₂Se₃ nanoparticles could be attributed to the high Se-volatilizing activities of the bacterial strains. Selenol-containing compounds as intermediates of Se-volatilizing metabolic pathways, such as methane selenol and selenocysteine, may play an important role in biosynthesis of Bi₂Se₃.