TiO₂ nanoparticles have increasingly been used in the various fields. However, it is these unique characteristics such as small sizes, large surface per mass, and high reactivity that TiO₂ nanoparticles can enter the human body quickly and then imposes potential risks on human health. In order to study the mechanisms underlying the effects of TiO₂ nanoparticles on acetylcholine esterase (AChE, EC3.1.1.7) of mice, ICR mices were injected with TiO₂ nanoparticles (5 nm) of various doses into the abdominal cavity daily for 14 d. We then examined AChE activity in vivo and in vitro and directly evident for interaction between TiO₂ nanoparticles and AChE using spectral methods. The results showed that TiO₂ nanoparticles could significantly activate AChE in vivo and in vitro. By spectral assays, the TiO₂ nanoparticles were determined to be directly bound to AChE, AChE had 1.6 strong binding sites for TiO₂ nanoparticles, and their binding constants of the binding sites were 2.56×10⁷ L•mol^－1, while the binding constants were 3.06×10⁶ L•mol^－1 for the weak binding sites. And TiO₂ nanoparticles induced the protein unfolding and secondary structure damage of AChE. It was concluded that the binding of TiO₂ nanoparticles altered AChe structure and function.

Key words: titanium dioxide nanoparticle, mice, acetylcholine esterase, spectral characteristics, structure-function