Microbial synthesis of nano-selenium and nano-titanium dioxide: mechanisms of selenite respiration

The unique physicochemical properties of nano-metals compared with those of non-nanomaterials have led to many investigations in recent decades. Nano-titanium dioxide has been chiefly applied in novel implant forms. Also, the structures of selenium-containing compounds play a critical role in the biological activity of these elements. According to recent studies, nano-selenium is not only less toxic, but also has a higher biological activity than selenium ions such as selenium (IV) (Se⁴⁺) and selenium (VI) (Se⁶⁺). Researchers have turned to green nanostructure synthesis due to the drawbacks of chemical techniques. This paper presents a literature review on recent advances in microbial synthesis methods for producing nano-selenium and nano-titanium dioxide. Despite numerous research articles on green nanoparticle production, little information has been provided on the microbial formation of titanium and selenium nanoparticles. This review paper focuses on the possible mechanism of nano-selenium production by selenium respiration. Although there are reports of microbial synthesis of these particles, their production by probiotic bacteria is of great value. Considering the compatibility of probiotic bacteria with the immune system and their tremendous applications in medicine, it is suggested to use them in combination with nano-titanium dioxide and nano-selenium for various ends such as implant scaffolds and food additives, respectively.