Biological effects on breast cancer cells of strong terahertz waves from a terahertz free-electron laser

It is of great importance to study the biological effects of terahertz (THz) waves on human cancer cells for their potential future applications in cancer therapy. However, only a few examples of distinct biological effects have been reported due to the lack of strong THz radiation sources. Here, we report our preliminary investigation using a strong THz source at 1.56 THz with an average power of ~ 10 W and an average intensity of ~129.1 mW/cm² working at a repetition rate of 10 Hz for its macro pulses with duration of ~1 ms and micro pulse duration of ~ 1 ps at a repetition rate of 54.17 MHz from a THz free-electron laser to investigate its biological effects on breast cancer cells in vitro. We observed significant morphological changes in breast cancer cells after 2 hours irradiation and apoptosis after 3 hours irradiation. Most notably, after 4 hours irradiation, we observed obvious cytolysis and the disappearance of most breast cancer cells in the center of the THz beam spot. It is suggested that these biological effects could be attributed mainly to the non-thermal effect of the strong THz waves according to our separate experimental results on the morphological changes of the breast cancer cells induced solely by heat. Our results indicate the potential to leverage the apoptosis and cytolysis of cancer cells induced by strong THz waves for future cancer treatment applications.