W1 PM Overview of Manufactured Nanomaterials and the Environment
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in Ballroom 1

(HUA-1117-739342) The Survival of Bacteria in the Presence of Photocatalytic Nano-TiO₂ Particles under Ambient Conditions.

Huang, C. P.¹, Mstzler, D. ¹, Erdem, A.¹, Lin, H. Y.¹, Huang, Y. C.², Cha, D.¹, Shah, I. ³, ¹ Department of Civil and Environmental Engineering, University of Delaware, Newark, DE 19716, USA² Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA³ Department of Material Science and Engineering, University of Delaware, Newark, DE 19716, USA

ABSTRACT- The effects of photocatalytic nano-TiO₂ on the survival or die-off of bacteria, exemplified by E. coli (e.g. TK2) were investigated under ambient conditions. Experimentally, a 28-h E. coli culture was exposed to photocatalytic nano-TiO₂ at various concentrations, e.g., 0 to 1 g/L and particle size, e.g., 5 to 100 nm both in darkness and the presence of a simulated solar light. Preliminary results indicated that E. coli underwent a two-stage response to nano-TiO₂ particles independent of light irradiation; a rapid decrease in population density within the first 10 min then slowly decreased upon extended treatment time, e.g., 30-60 min. No significant difference in terms of bacterial die-off was observed in the size range of 5 to 25 nm. An optimal particle concentration for the survival of E. coli was observed, e.g. 0.01 g/L. The die-off of E. coli increased with increasing particle concentration to the optimal level, ca. 0.01 mg/L then decreased upon further increase in particle concentration, e.g. > 0.01 g/L. Apparently, the presence of nano-TiO₂ particles exhibited both beneficial and adverse effects. The ability of TiO₂ to adsorb nutrients benefited the E. coli. However, the presence of TiO₂ also brought about adverse effects such as blocking the cell membrane, which impeded the transport of nutrients and metabolite residues between the intra- and the extra-cellular environment. The presence of light irradiation significantly enhanced the killing of E. coli due to additional photocatalytic activity. Photocatalytic reactions generated hydroxyl radical, which is strong oxidation agent that can cause great stress and damage to the cell. Cell damage was observed in terms of lipid peroxidation (e.g., production of malondialdehyde, MDA), cellular respiration (e.g., reduction of 2,3,5-triphenyltetrazolium chloride, TTC) and antioxidant enzyme (e.g., glutathione-S-transferase). Results indicated increase in the generation of MDA, TTC and GST upon exposure of E. coli to nano-TiO₂; photocatalytic activity markedly increased the production of MDA, TTC and GST. (EPA STAR Project #R-83177101)

Key words: TiO₂, Nano-photocatalyst, Bacterial die-off, E. coli