title: Broad-Spectrum Antimicrobial Effects of Photocatalysis Using Titanium Dioxide Nanoparticles Are Strongly Potentiated by Addition of Potassium Iodide.
abstract: Photocatalysis describes the excitation of titanium dioxide nanoparticles (a wide-band gap semiconductor) by UVA light to produce reactive oxygen species (ROS) that can destroy many organic molecules. This photocatalysis process is used for environmental remediation, while antimicrobial photocatalysis can kill many classes of microorganisms and can be used to sterilize water and surfaces and possibly to treat infections. Here we show that addition of the nontoxic inorganic salt potassium iodide to TiO2 (P25) excited by UVA potentiated the killing of Gram-positive bacteria, Gram-negative bacteria, and fungi by up to 6 logs. The microbial killing depended on the concentration of TiO2, the fluence of UVA light, and the concentration of KI (the best effect was at 100 mM). There was formation of long-lived antimicrobial species (probably hypoiodite and iodine) in the reaction mixture (detected by adding bacteria after light), but short-lived antibacterial reactive species (bacteria present during light) produced more killing. Fluorescent probes for ROS (hydroxyl radical and singlet oxygen) were quenched by iodide. Tri-iodide (which has a peak at 350 nm and a blue product with starch) was produced by TiO2-UVA-KI but was much reduced when methicillin-resistant Staphylococcus aureus (MRSA) cells were also present. The model tyrosine substrate N-acetyl tyrosine ethyl ester was iodinated in a light dose-dependent manner. We conclude that UVA-excited TiO2 in the presence of iodide produces reactive iodine intermediates during illumination that kill microbial cells and long-lived oxidized iodine products that kill after light has ended.
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA Department of Dermatology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Ying-Ying
authors.initials: YY
authors.lastname: Huang
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA Korean Advanced Institute of Science and Technology, Seoul, South Korea.
authors.forename: Hwanjun
authors.initials: H
authors.lastname: Choi
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA Graduate School of Pharmaceutical Science, University of Tokyo, Tokyo, Japan.
authors.forename: Yu
authors.initials: Y
authors.lastname: Kushida
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA Department of Dermatology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Brijesh
authors.initials: B
authors.lastname: Bhayana
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA Department of Dermatology, Harvard Medical School, Boston, Massachusetts, USA Center of Digital Dentistry, Peking University School and Hospital of Stomatology, Beijing, People's Republic of China.
authors.forename: Yuguang
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA Department of Dermatology, Harvard Medical School, Boston, Massachusetts, USA Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts, USA Hamblin@helix.mgh.harvard.edu.
authors.forename: Michael R
authors.identifier: 0000-0001-6431-4605
authors.initials: MR
authors.lastname: Hamblin
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D005658:Fungi / Q000187:drug effects* / Q000528:radiation effects; D006090:Gram-Negative Bacteria / Q000187:drug effects* / Q000528:radiation effects; D006094:Gram-Positive Bacteria / Q000187:drug effects* / Q000528:radiation effects; D008826:Microbial Sensitivity Tests; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D011193:Potassium Iodide / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000737:chemistry; D014025:Titanium / Q000494:pharmacology*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000737:chemistry; D014466:Ultraviolet Rays
chemical_list: D000900:Anti-Bacterial Agents; D017382:Reactive Oxygen Species; C009495:titanium dioxide; D011193:Potassium Iodide; D014443:Tyrosine; C007651:ethyl N-alpha-acetyl-tyrosinate; D014025:Titanium