Mechanism of Photogenerated Reactive Oxygen Species and Correlation with the Antibacterial Properties of Engineered Metal-Oxide Nanoparticles

Abstract

Oxidative stress induced by reactive oxygen species (ROS) is one of the most important antibacterial mechanisms of engineered nanoparticles (NPs). To elucidate the ROS generation mechanisms, we investigated the ROS production kinetics of seven selected metal-oxide NPs and their bulk counterparts under UV irradiation (365 nm). The results show that different metal oxides had distinct photogenerated ROS kinetics. Particularly, TiO(2) nanoparticles and ZnO nanoparticles generated three types of ROS (superoxide radical, hydroxyl radical, and singlet oxygen), whereas other metal oxides generated only one or two types or did not generate any type of ROS. Moreover, NPs yielded more ROS than their bulk counterparts likely due to larger surface areas of NPs providing more absorption sites for UV irradiation. The ROS generation mechanism was elucidated by comparing the electronic structures (i.e., band edge energy levels) of the metal oxides with the redox potentials of various ROS generation, which correctly interpreted the ROS generation of most metal oxides. To develop a quantitative relationship between oxidative stress and antibacterial activity of NPs, we examined the viability of E. coli cells in aqueous suspensions of NPs under UV irradiation, and a linear correlation was found between the average concentration of total ROS and the bacterial survival rates (R(2) = 0.84). Although some NPs (i.e., ZnO and CuO nanoparticles) released toxic ions that partially contributed to their antibacterial activity, this correlation quantitatively linked ROS production capability of NPs to their antibacterial activity as well as shed light on the applications of metal-oxide NPs as potential antibacterial agents.

Quantitative Analysis of Reactive Oxygen Species Photogenerated on Metal Oxide Nanoparticles and Their Bacteria Toxicity: The Role of Superoxide Radicals

“…In additional, • OH maximum generation concentration was about 150 nM, which was also lower than the reported. 22 This is probably again due to the large difference in illumination duration between the two measurements, as well as the type of nTiO 2 used. Figure 1d shows the H 2 O 2 formation kinetics of different NPs.…”

Adsorption of MS2 on oxide nanoparticles affects chlorine disinfection and solar inactivation

“…NaCl solution (pH ¼ 6.8) were all analyzed on a Zetasizer nano ZS instrument (Malvern Instruments, UK) with the results summarized in Table 1 and more detailed characterization reported previously (Li et al, 2012b;Zhang et al, 2009Zhang et al, , 2008.…”

“…The MS2 concentrations in the presence of 10 mg L À1 NPs were all reduced compared with the dark control. In particular, TiO 2 and ZnO NPs both displayed strong MS2 inactivation compared with the solar exposure control, probably because of their ability to generate ROS under UV excitation (Li et al, 2014(Li et al, , 2012b. Common radical species are hydroxyl radicals (OH), singlet oxygen (…”

“…On the other hand, positive benefits of engineered NPs are also highlighted by many studies, which incorporated metallic NPs (e.g., nanosilver) to remove pathogenic microorganisms (Li et al, 2008a(Li et al, , 2014. Particularly, many metal NPs and carbonaceous nanomaterials such as fullerene are capable of deactivating viruses or bacteriophages mainly due to the ability to generate reactive oxygen species (ROS) when irradiated by UV light (Cho et al, 2009;Li et al, 2012b;Zhang et al, 2013). A brief literature survey of recent studies on inactivation of viruses or phages by NPs is tabulated in Table S1 of the supporting information (SI).…”

Synthesis and Characterization of Various Metal Ions Doped CeO2 Nanoparticles Derived from the Azadirachta Indica Leaf Extracts

“…ROS include the most reactive hydroxyl radical ( • OH), less toxic superoxideanion radical ( −• O 2 ) and singlet oxygen ( 1 O 2 ) with a weaker oxidizer, contributing to the major oxidative stress in biological systems 18 . ROS generation is closely associated with the efficiency of a photocatalyst, depending on the generation rate, rate of migration and energy levels of the photoexcited electron-hole pairs.…”