Real time, in situ observation of the photocatalytic inactivation of Saccharomyces cerevisiae cells

• Palladium-modified nitrogen-doped titanium oxidephotocatalyst (TiON/PdO)
• Effective visible-light photocatalytic disinfection of yeast cells by TiON/PdO
• Real time, in situ observation technique was developed for photocatalytic disinfection.
• The fluorescence/phase contrast microscope with a photocatalytic micro-reactor
• Yeast cell disinfection happened before the cell structure collapsed.

An in situ microscopy technique was developed to observe in real time the photocatalytic inactivation process of Saccharomyces cerevisiae (S. cerevisiae) cells by palladium-modified nitrogen-doped titanium oxide (TiON/PdO) under visible light illumination. The technique was based on building a photocatalytic micro-reactor on the sample stage of a fluorescence/phase contrast microscopy capable of simultaneously providing the optical excitation to activate the photocatalyst in the micro-reactor and the illumination to acquire phase contrast images of the cells undergoing the photocatalytic inactivation process. Using TiON/PdO as an example, the technique revealed for the first time the vacuolar activities inside S. cerevisiae cells subjected to a visible light photocatalytic inactivation. The vacuoles responded to the photocatalytic attack by the first expansion of the vacuolar volume and then contraction, before the vacuole disappeared and the cell structure collapsed. Consistent with the aggregate behavior observed from the cell culture experiments, the transition in the vacuolar volume provided clear evidence that photocatalytic disinfection of S. cerevisiae cells started with an initiation period in which cells struggled to offset the photocatalytic damage and moved rapidly after the photocatalytic damage overwhelmed the defense mechanisms of the cells against oxidative attack.

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