Destruction of Deinococcus geothermalis biofilm by photocatalytic ALD and sol-gel TiO2 surfaces

The aim of the present work was to explore possibilities of photocatalytic TiO₂ coating for reducing biofilms on non-living surfaces. The model organism, Deinococcus geothermalis, known to initiate growth of durable, colored biofilms on machine surfaces in the paper industry, was allowed to form biofilms on stainless steel, glass and TiO₂ film coated glass or titanium. Field emission electron microscopy revealed that the cells in the biofilm formed at 45°C under vigorous shaking were connected to the surface by means of numerous adhesion threads of 0.1--0.3 μm in length. Adjacent cells were connected to one another by threads of 0.5--1 μm in length. An ultrastructural analysis gave no indication for the involvement of amorphous extracellular materials (e.g., slime) in the biofilm. When biofilms on photocatalytic TiO₂ surfaces, submerged in water, were exposed to 20 W h m⁻² of 360 nm light, both kinds of adhesion threads were completely destroyed and the D. geothermalis cells were extensively removed (from >10⁷ down to below 10⁶ cells cm⁻²). TiO₂ films prepared by the sol-gel technique were slightly more effective than those prepared by the ALD technique. Doping of the TiO₂ with sulfur did not enhance its biofilm-destroying capacity. The results show that photocatalytic TiO₂ surfaces have potential as a self-cleaning technology for warm water using industries.