Charge-switchable magnetic separation and characterization of food additive titanium dioxide nanoparticles from commercial food.

Growing concerns about the potential health effects of nanoscale titanium dioxide (TiO) have necessitated the need for monitoring the size distribution and physicochemical properties of food additive TiO that are present in commercial food. Acid digestion is by far the most widely used method to remove interfering food matrices, but the highly corrosive nature of the reaction could alter the physicochemical properties of the TiO, which may give a skewed information about the materials. Here, we report an effective approach to extract intact form of food additive TiO nanoparticles from processed food through charge-charge interaction between TiO particles and charge-switchable starch magnetic beads (PL@SMBs), of which the captured TiO is readily harvested by switching the surface charge of PL@SMBs to neutral. The size and surface property of extracted TiO were shown to be well maintained due to the mild nature of the reaction. The extracted TiO particles from 10 commercial processed food showed a size distribution from 40 to 250 nm with a mean diameter of 115 nm, of which 22 % of them were less than 100 nm. The extracted TiO did not exhibit short-term cytotoxicity, but induced cellular oxidative stress at high concentration.