Synthesis of hollow silica microparticles from bacterial templates

Hollow inorganic particles have attracted great interest because of their unique physicochemical properties. In this study, hollow silica microparticles were prepared using a rod-shaped gram-negative bacterium, Escherichia coli (KP7600), as a biological template. Silica nanoparticles were generated in addition to coated biological templates when the reaction rate was increased, so control of reaction rate is important for coating silica smoothly onto the bacterial surface. Silica coating was also carried out using the fixed cells (with and without internal water) using glutaraldehyde as templates. When the fixed cells without internal water were used as templates, no rod-shaped particles were observed after calcination of the synthesized particles. By contrast, silica hollow particles were formed using the fixed cells with internal water as templates. This means that the internal water inside biological cells acts as an initiator for hydrolysis of tetraethyl orthosilicate (TEOS) and results in the formation of smooth silica shell surface and indicates that the use of dry cultured bacteria templates is not required. Thus, there is a significant benefit in using gram-negative bacteria as templates for producing hollow silica microparticles, compared with the method using dried gram-positive bacteria templates.