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.