Numeration methods for targeting photoactive materials in the UV-A photocatalytic removal of microorganisms

Abstract

This tutorial review reports on the different numeration methods for evaluating the efficiency of the photocatalytic action on microorganisms. Here we put forward the advantages and drawbacks of the standard methods such as the plate count, the fluorescence techniques and the Most Probable Number method for determining the biocidal photocatalytic activity and thus selecting efficient photocatalytic materials among complex systems. We highlight that bacterial spores are a representative and suitable tool for meeting the restrictive requirements resulting from the complex use of living matter instead of chemical targets.

TiO 2 Photocatalysis Damages Lipids and Proteins in Escherichia coli

“…The photogenerated charges take part in reduction and oxidation reactions at the particle surface (12,14). In particular, holes and electrons are, respectively, reacting with adsorbed water and dioxygen molecules to form ROS, such as the ·OH hydroxyl radical and the O 2 · Ϫ superoxide radical anion, respectively.…”

Comparative studies of photocatalytic and photoelectrocatalytic inactivation of E. coli in presence of halides

“…The BacLight TM kit method is a double staining method based on the non-selectivity of SYTO 9 stain towards the integrity of cell membranes and the selectivity of the PI stain towards damaged cell membranes. That is, SYTO 9 can penetrate the cell membrane whatever its integrity to form complex with the living cell DNA to fluoresce green, whereas PI is only able to enter the damaged cells, reducing SYTO 9 fluorescence when both dyes are present, which makes the dead cells emit red light [11]. It should be noted that the orange colored cell images shown in Fig.…”

“…It is well-known that a photocatalytically generated hole at TiO 2 valence band is a more powerful oxidant than that of AOSs. In a PC system, the photoholes are mainly consumed to generate AOSs rather than directly reacting with the target species [9,11,13]. However, the prolonged photoholes' lifetime in a PEC system can directly react with target species to significantly enhance the photocatalytic efficiency [30].…”

“…A large body of work has since been carried out. Up till now, the photocatalytic inactivation of a wide range of microorganisms has been reported [8][9][10][11][12][13][14][15][16]. In their initial study, Matsunaga and co-workers investigated the photocatalytic disinfection of Escherichia coli, Lactobacillus acidophilus and Sacharomyces cerevisae using TiO 2 /Pt as the photocatalyst [7].…”

“…Despite the significant progress, some details of killing mechanisms are still under investigation. Nevertheless, there has been a commonly accepted view that the bactericidal effect of TiO 2 photocatalysis is achieved via the photocatalytically generated AOSs [9,11,13]. These AOSs possess a shorter life in aqueous environments and less effective to cause damage to the polymeric membrane materials [10,13,23].…”