Mechanism of Escherichia coli inactivation on palladium-modified nitrogen-doped titanium dioxide

The cellular responses of Escherichia coli to visible light photocatalysis were characterized by chemical, optical, electron-beam, and surface-force techniques, to elucidate the mechanisms of photocatalytic inactivation of E. coli on PdO/TiON fiber. The characterization techniques included chemical assays, fluorescence microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Fluorescence microscopy using the Live/Dead BacLight™ kit indicates that the photocatalytic treatment resulted in severe membrane damage to the E. coli cells. SEM, AFM and TEM revealed drastic defects in the morphology and internal sub-structure of the bacterial cells after the treatments. Combining data from our previous reports on the antimicrobial properties of visible-light-activated PdO/TiON photocatalyst, the present results point to oxidative attack from the exterior to the interior of the bacteria by hydroxyl radicals as the primary mechanism of photocatalytic inactivation.