Preparation of DNA-adsorbed TiO2 particles--augmentation of performance for environmental purification by increasing DNA adsorption by external pH regulation.

We have previously developed a novel photocatalyst, DNA-attached titanium dioxide (DNA-TiO(2)), useful for the recovery and decomposition of chemicals [Suzuki et al. Environ. Sci. Technol. 42, 8076, 2008]. Chemicals accumulated in DNA near the surface of TiO(2) and were degraded under UV light. The efficiency of their removal was dependent on the amount of DNA adsorbed on TiO(2), indicating the attachment of larger amounts of DNA to result in higher efficiency. In this study, we succeeded in improving the performance of DNA-TiO(2) by increasing the amount of DNA adsorbed by regulating the external pH. The adsorption of DNA by TiO(2) dramatically increased at pH2, to about fourfold that at other pH values (pH4-10). Repeating the process of DNA addition increased the adsorption further. The attached DNA was stable on the surface of TiO(2) at pH2-10 and 4-56 degrees C, the same as DNA-TiO(2) prepared at pH7. As the DNA-TiO(2) prepared at pH2 retained much DNA on its surface, chemicals (methylene blue, ethidium bromide, etc.) which could intercalate or react with DNA were effectively removed from solutions. The photocatalytic degradation was slow at first, but the final degradation rate was higher than for non-adsorbed TiO(2) and DNA-TiO(2) prepared at pH7. These results indicated that preparation of DNA-TiO(2) at pH2 has advantages in that much DNA can be attached and large amounts of chemicals can be concentrated in the DNA, resulting in extensive decomposition under UV light.