DNA can sediment TiO2 particles and decrease the uptake potential by mammalian cells

Titanium dioxide (TiO2) is an important material used in a broad range of industries. As TiO2 particles used in industries have recently become smaller as technology develops, problems specific to small size are increasing. One such problem is the difficulty of recovering TiO2 particles suspended in solution. Particles not recovered during their manufacture would be released in the environment and might be taken up by living organisms, leading to “small-size specific toxicity”, which has recently become a concern in numerous industries. To prevent environmental release of small-size TiO2, separation and complete recovery of the particles are important. In this study, we showed that DNA could be used to separate TiO2 particles (60–500 nm) from an aqueous solution. Although TiO2 particles (20 mg/10 ml) were kept in suspension in a standing solution for 72 h, addition of small amounts of DNA (25–100 μg/10 ml) completely sedimented all particles within 4 h. Analysis with transmission electron microscopy suggested that the enhanced sedimentation with DNA was due to the formation of aggregates of TiO2 particles with DNA. Conveniently, DNA-treated TiO2 particles had difficulty translocating into human cell lines (keratinocytes and skin fibroblasts), suggesting that “small-size specific toxicity” can be prevented. DNA is a useful tool for separating TiO2 particles which would prevent “small-size specific toxicity” by allowing quick and complete recovery and suppression of uptake by living organisms.