Effects of Material Morphology on the Phototoxicity of Nano-TiO₂ to Bacteria

Abstract

Nanostructured titania (nano-TiO2) is produced in diverse shapes, but it remains largely unknown how tuning the morphology of nano-TiO2 may alter its toxicity. Herein, we show that material morphology plays a critical role in regulating the phototoxicity of nano-TiO2 to bacteria. Low-dimensional nano-TiO2, including nanotubes, nanorods, and nanosheets, were synthesized hydrothermally, and their effects on the bacterial viability of Escherichia coli and Aeromonas hydrophila were compared to spherical nanostructures (anatase nanospheres and P25). Results reveal that TiO2 nanotubes and nanosheets are less phototoxic than their rod- and sphere-shape counterparts under simulated solar irradiation. None of the tested nano-TiO2 shows toxicity in the dark. In contrast to their diminished phototoxicity, however, TiO2 nanotubes and nanosheets exhibit comparable or even higher photoactivity than other nanostructures. Observations by scanning transmission electron microscopy suggest that material morphology influences nano-TiO2 phototoxicity by governing how nano-TiO2 particles align at the bacterial cell surface. Overall, when comparing materials with different morphologies and dimensionality, nano-TiO2 phototoxicity is not a simple function of photocatalytic reactivity or ROS production. Instead, we propose that the evaluation of nano-TiO2 phototoxicity encompasses a three-pronged approach, involving the intrinsic photoactivity, aggregation of nano-TiO2, and the nano-TiO2/bacteria surface interactions.

Recent Advances in the Synthesis of Metal Oxide Nanofibers and Their Environmental Remediation Applications

“…While ZnO shows strong antibacterial properties under ambient radiation, TiO2 generally responds under UV radiation [169,170]. Methods for completing the photocatalysis of waterborne microorganisms into visible and solar light energy have been obtained by making composites, design of core-shell type nanostructures, nanoparticle doping, surface wettability patterning, offset printing, or increase of crystal defect [170].…”

Highly synergistic antimicrobial activity of spherical and flower-like hierarchical titanium dioxide/silver composites

“…Previous studies suggested that the antibacterial activities of TiO 2 -based materials were attributed to photocatalytic activity for generating reactive oxygen species (ROS), such as •OH radicals [37] . These ROS may produce oxidative stress and then attack membrane lipids, ultimately leading to membrane or DNA damage.…”

One-Time Addition of Nano-TiO2 Triggers Short-Term Responses in Benthic Bacterial Communities in Artificial Streams

“…The decrease in bacterial abundance was first noted 1 day after addition, but bacterial numbers returned to control levels within 3 weeks. Multiple previous studies have demonstrated the toxicity of nano-TiO 2 to bacteria [11,15,[17][18][19][20] and have confirmed that the toxicity of nano-TiO 2 is due primarily to its production of ROS when illuminated [11], but these studies have been conducted with both the bacteria and nano-TiO 2 particles mixed in suspension. The toxicity of nano-TiO 2 to sediment-associated organisms that was observed in this study under realistic environmental conditions is novel, and it is significant because of the ecological importance of benthic microbial communities.…”

“…Nano-TiO 2 has been shown to be toxic to aquatic organisms, including fish [12][13][14], invertebrates [15][16][17], bacteria [11,15,[17][18][19][20], cyanobacteria [21,22], and algae [22][23][24][25][26]. Most studies demonstrating the toxicity of nano-TiO 2 have been conducted with model organisms under laboratory conditions, although a few have attempted to model more realistic environmental conditions.…”