Conventional photocatalysts are primarily stimulated using ultraviolet (UV) light to elicit reactive oxygen species and have wide applications in environmental and energy fields, including self-cleaning surfaces and sterilization. Because UV illumination is hazardous to humans, visible light-responsive photocatalysts (VLRPs) were discovered and are now applied to increase photocatalysis. However, fundamental questions regarding the ability of VLRPs to trigger DNA mutations and the mutation types it elicits remain elusive. Here, through plasmid transformation and β-galactosidase α-complementation analyses, we observed that visible light-responsive platinum-containing titania (TiO 2 ) nanoparticle (NP)-mediated photocatalysis considerably reduces the number of Escherichia coli transformants. This suggests that such photocatalytic reactions cause DNA damage. DNA sequencing results demonstrated that the DNA damage comprises three mutation types, namely nucleotide insertion, deletion and substitution; this is the first study to report the types of mutations occurring after photocatalysis by TiO 2 -VLRPs. Our results may facilitate the development and appropriate use of new-generation TiO 2 NPs for biomedical applications. Nanomaterials 2017, 7, 2 2 of 13 holes (electron vacancy) in the valence band. The excited electrons and holes are trapped on the TiO 2 surfaces. These electrons and holes may then recombine and release energy as light or heat, resulting in inefficient photocatalysis. Alternatively, they may react with atmospheric water and oxygen to yield a reactive oxygen species (ROS), such as hydrogen peroxide, hydroxyl radicals (·OH) or superoxide anions (O 2 − ) [5]. These ROS are powerful biocides that eliminate pathogenic microorganisms. However, human exposure to UV light at bactericidal levels can considerably damage skin and eye tissues [6, 7] , which limits the use of conventional UV light-induced TiO 2 substrates in environments where human exposure may occur. This problem can be resolved by impurity doping TiO 2 with different elements, such as carbon, sulfur, nitrogen and silver, which shifts the excitation wavelength from the UV region to the visible light region [2, [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] . Simultaneously, this process may also reduce the recombination rates of the electron and hole pairs. Visible light-responsive antibacterial photocatalysts (which have a higher quantum efficiency under sunlight than do UV light-responsive photocatalysts) can be safely used in indoor settings to prevent human exposure to UV light [2, [8] [9] [10] [11] [13] [14] [15] [16] . The molecular targets of photocatalysis in bacteria (e.g., DNA, RNA, protein and cell membrane) and the intensity at which these are affected remain unclear. Because photocatalytic reactions involve both oxidation and reduction [20, 21] , damage observed in the target microorganisms differs from that observed with traditional disinfectants, which involve either oxidation or reduction. This is probably the reason that we previously observed a unique pattern of photocatalysis-induced bacterial destruction [2, 10] . UV light-responsive TiO 2 induces DNA damage without specified temperature control [22, 23] ; however, UV light alone can also induce DNA mutation and damage [24, 25] . In addition, photocatalysis at room temperature (25 • C) induces more DNA damage than that at 4 • C (Figure 1 ). The absorption of illuminated light energy can produce heat; thus, illumination-induced heat also potentially has a major role in triggering DNA damage. However, visible light-responsive photocatalyst (VLRP)-induced DNA mutations have not been clearly characterized thus far. Therefore, the exact photocatalysis-induced DNA damage, without perturbations of the effects of heat and UV light, warrants further investigation. In the present study, we used a previously-reported visible light-responsive platinum-containing titania (TiO 2 -Pt) photocatalytic nanoparticle (NP) [11, 16] to address this question. Our data revealed that VLRPs can induce DNA mutations.
Output: Visible Light-Responsive Platinum-Containing Titania Nanoparticle-Mediated Photocatalysis Induces Nucleotide Insertion, Deletion and Substitution Mutations