Using an AIST original technique for quantifying the intracellular amount of carbon nanotube (CNT) that uses the near-infrared absorption measurement, the researchers measured the amount change of super-growth single-walled CNT (SG-CNTs) in macrophages over time, and clarified that SG-CNT is biodegradable, in collaboration with Zeon Corporation.

Conceptual diagram of CNT biodegradation in a macrophage

With the increase of CNT industrialization, the concern regarding the harmful effects on the public health has attracted much attention due to that CNTs are possible to be exposed to the environment, absorbed by animal and human bodies, and accumulated in immune tissues. Clarification of the biodegradation properties of CNTs is important for understanding their long-term safety. However, most of the studies on the biodegradation of CNTs are performed qualitatively, and the details are still not clear.

By utilizing the characteristic of CNTs that absorbs near-infrared light, the researchers have developed a technique to measure the amount change of CNT inside of macrophage cells over time. After SG-CNTs were administered and internalized into macrophage cells, the cells were lysed and the amount of SG-CNTs in the lysate was measured based on the near-infrared light absorbance. The results showed that the intracellular amount of SG-CNTs decreased over time. In addition, the amount of reactive oxygen species (ROS) generated by macrophages after SG-CNT uptake was measured. It was found that the decrease tendency of ROS coincides with that of the amount decrease of SG-CNTs inside of cells, suggesting that the biodegradation of SG-CNT in macrophages is caused by ROS.

The researchers will clarify the relationship between biodegradability of CNTs and their physicochemical properties such as size and surface modifications, and develop methods to enable prediction and control of biodegradability of CNTs.