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.