Effect of TiO2 nanoparticles on the thermal stability of native DNA under UV irradiation

TiO2 nanoparticles (NPs) are widely used in the environmental engineering, medicine, chemical and food industries due to their unique photocatalytic and biocidal properties. NPs may generate reactive oxygen species and, hence, have the toxic effect on the living cells via oxidative stress. An external UV irradiation may magnify the photocatalytic properties of TiO2 NPs. In this regard, we have analyzed the influence of TiO2 NPs on the conformation and thermal stability of native DNA in a buffer suspension without and under UV irradiation exploiting absorption spectroscopy and thermal denaturation in the range of 20-94 degrees C. The TiO2 NPs size distribution and polydispersity index were examined by dynamic light scattering (DLS) and confirmed by TEM. The DNA:TiO2 NPs assemblies were revealed and characterized by DLS and TEM. Upon heating the DNA suspension with TiO2 NPs from about 25 to 44 degrees C we have observed decreasing the hyperchromicity coefficient (h) on the DNA melting curves. That is explained by the intensive formation of the DNA:TiO2 NPs assemblies. We have revealed, that partial DNA disordering appears at initial contacts with NPs. DNA binding to TiO2 NPs is manifested in the change of the DNA melting temperature (T-m). We showed that the performed UV treatment of DNA during 3 h leads to partial unwinding of the biopolymer structure. The NPs injection to the biopolymer suspension induced the additional effect on the DNA thermal stability under UV irradiation. The performed analysis of the experimental data suggests that the nature of the impact of NPs on the biopolymer is complex.