title: New evidence for TiO2 uniform surfaces leading to complete bacterial reduction in the dark: critical issues.
abstract: This study presents new evidence for the events leading to Escherichia coli reduction in the absence of light irradiation on TiO2-polyester (from now on TiO2-PES. By transmission electron microscopy (TEM) the diffusion of TiO2 NP's aggregates with the E. coli outer lipo-polyssacharide (LPS) layer is shown to be a prerequisite for the loss of bacterial cultivability. Within 30 min in the dark the TiO2 aggregates interact with E. coli cell wall leading within 120 min to the complete loss of bacterial cultivability on a TiO2-PES 5% TiO2 sample. The bacterial reduction was observed to increase with a higher TiO2 loading on the PES up to 5%. Bacterial disinfection on TiO2-PES in the dark was slower compared to the runs under low intensity simulated sunlight light irradiation. The interaction between the TiO2 aggregates and the E. coli cell wall is discussed in terms of the competition between the TiO2 units collapsing to form TiO2-aggregates at a physiologic pH-value followed by the electrostatic interaction with the bacteria surface. TiO2-PES samples were able to carry repetitive bacterial inactivation. This presents a potential for practical applications. X-ray photoelectron spectroscopy (XPS) evidence was found for the reduction of Ti4+ to Ti3+ contributing to redox interactions between TiO2-PES and the bacterial cell wall. Insight is provided into the mechanism of interaction between the E. coli cell wall and TiO2 NP's. The properties of the TiO2-PES surface like percentage atomic concentration, TiO2-loading, optical absorption, surface charge and crystallographic phases are reported in this study.
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, EPFL-SB-ISIC-GPAO, Station 6, CH-1015, Lausanne, Switzerland; Faculty of Chemistry, University of Belgrade, Studentski trg 12, Belgrade, Serbia.
authors.forename: Jelena
authors.initials: J
authors.lastname: Nesic
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, EPFL-SB-ISIC-GPAO, Station 6, CH-1015, Lausanne, Switzerland. Electronic address: sami.rtimi@epfl.ch.
authors.forename: Sami
authors.initials: S
authors.lastname: Rtimi
authors.affiliation: EPFL SB CIME-MXC039, Station 12, CH-1015 Lausanne, Switzerland.
authors.forename: Danièle
authors.initials: D
authors.lastname: Laub
authors.affiliation: Faculty of Chemistry, University of Belgrade, Studentski trg 12, Belgrade, Serbia.
authors.forename: Goran M
authors.initials: GM
authors.lastname: Roglic
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, EPFL-SB-ISIC-GPAO, Station 6, CH-1015, Lausanne, Switzerland. Electronic address: cesar.pulgarin@epfl.ch.
authors.forename: Cesar
authors.initials: C
authors.lastname: Pulgarin
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, EPFL-SB-ISIC-LPI, Bat Chimie, Station 6, CH1015, Lausanne, Switzerland.
authors.forename: John
authors.initials: J
authors.lastname: Kiwi
mesh_terms: D004926:Escherichia coli / Q000187:drug effects* / Q000528:radiation effects; D008027:Light; D046529:Microscopy, Electron, Transmission; D014025:Titanium / Q000494:pharmacology*
chemical_list: C009495:titanium dioxide; D014025:Titanium
keywords: Aggregation/co-aggregation; Colloidal TiO(2); Dark run; E. coli; Interface charge transfer