Does nanoparticle activity depend upon size and crystal phase?

Abstract

A method to investigate the dependence of the physicochemical properties of nanoparticles (e.g. size, surface area and crystal phase) on their oxidant generating capacity is proposed and demonstrated for TiO 2 nanoparticles. Gas phase synthesis methods that allow for strict control of size and crystal phase were used to prepare TiO 2 nanoparticles. The reactive oxygen species (ROS) generating capacity of these particles was then measured. The size dependent ROS activity was established using TiO 2 nanoparticles of 9 different sizes (4 -195 nm) but the same crystal phase. For a fixed total surface area, an S-shaped curve for ROS generation per unit surface area was observed as a function of particle size. The highest ROS activity per unit area was observed for 30 nm particles, and observed to be constant above 30 nm. There was a decrease in activity per unit area as size decreased from 30 nm to 10 nm; and again constant for particles smaller than 10 nm. The correlation between crystal phase and oxidant capacity was established using TiO 2 nanoparticles of 11 different crystal phase combinations but similar size. The ability of different crystal phases of TiO 2 nanoparticles to generate ROS was highest for amorphous, followed by anatase, and then anatase/rutile mixtures, and lowest for rutile samples. Based on evaluation of the entire dataset, important dose metrics for ROS generation are established. Their implications of these ROS studies on biological and toxicological studies using nanomaterials are discussed.

Earthworm Sublethal Responses to Titanium Dioxide Nanomaterial in Soil Detected by 1H NMR Metabolomics

“…For the nanosized material in their study, they characterized and reported the primary particle size (30 nm diameter) and crystallinity (73% anatase and 27% rutile); however, for the bulk control only the nominal diameter (40 μm) was reported, and no information regarding the crystal phase of the material was given. 12 As it has been suggested that the crystal phase of TiO 2 may be more important than particle size for predicting toxicity, 68,72 it is possible that a difference in the crystallinity of the two TiO 2 materials used may have significantly confounded their results regarding the role of particle size. Of the two main industrially relevant crystal phases of TiO 2 (anatase and rutile), evidence suggests that the anatase form used in the current study may be more toxic.…”

“…73 Even at larger sizes (up to 195 nm diameter), anatase TiO 2 has demonstrated potential to generate reactive oxygen species. 68 In addition, Adams et al 71 noted that anatase TiO 2 materials with mean measured particle diameters of between 300 and 1000 nm significantly impaired growth in both Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria, with no apparent reduction in toxicity related to increased particle size. This demonstrates that although micrometer-sized TiO 2 materials (>100 nm) are generally considered nontoxic, 1 they can generate toxic responses in certain living organisms, at least when anatase phase materials are considered.…”

(Q)SAR modelling of nanomaterial toxicity: A critical review

“…(Jiang, et al, 2008) has investigated the effect of crystallinity on NP activity by comparing ROS generating capacity of TiO 2 NPs of similar size but different crystal phases (amorphous, anatase, rutile and anatase/rutile mixtures). The study has demonstrated that amorphous samples showed the highest level of ROS activity followed by pure anatase and anatase/rutile mixtures while pure rutile produced the lowest level of ROS.…”

Influence of titanium dioxide modification on the antibacterial properties

“…On the other hand, the generation of reactive oxygen species (ROS) -the main factor caused oxidative stress in bacteria cells depends on crystal structure and surface area. According to Jiang et al 31 , ROS generation is associated with the number of defect sites per surface area, and an S-shaped curve was observed as a function of particle size. The ability of titania nanoparticles to generate ROS grows as follows: amorphous > anatase > anatase/rutile mixtures > rutile.…”