Green Synthesis of Vanadium Dioxide Nanoparticles by <i>Shewanella</i> sp. Strain HN-41

Vanadium dioxide (VO₂) nanoparticles have various application potentials such as smart windows and electronic devices due to their unique phase transition properties. However, conventional VO₂ synthesis methods require harsh conditions and toxic reducing agents, leading to environmental problems. In this study, we developed an eco-friendly method to biosynthesize VO₂ nanoparticles using <i>Shewanella</i> sp. strain HN-41 under anaerobic conditions at 30°C and neutral pH. Morphological observations revealed that biogenic VO₂ nanoparticles with an average size of 4.3 nm were in the form of granules presented inside and outside the cells. These nanoparticles were identified as VO₂ by differential scanning calorimetry (DSC) analysis, which showed a phase transition temperature of 61.9°C, consistent with that of VO₂. Furthermore, we observed an active formation of vesicles containing VO₂ nanoparticles by the cross-sectioned transmission electron microscopy (TEM) analysis. Thus, in addition to the direct extracellular formation of VO₂ nanoparticles through anaerobic respiration, bacterial membrane vesicles likely play a role in expelling nanoparticles from the cell, potentially mitigating their toxicity. These findings highlight metal reducing bacteria could be a biological green agent for the production of valuable VO₂ nanoparticles under anaerobic environmental conditions.