Researchers in Japan have discovered a mechanism by which THz radiation can cause biological changes several millimetres inside humans.

This kind of electromagnetic radiation, at frequencies between microwaves and x-rays, is being considered as a less-invasive alternative to x-rays for medical and security scanning, and perhaps medical therapies for skin.

THz radiation, which is technically difficult to generate, handle and receive, has recently been found to affect biological materials and so cannot be considered non-invasive. However, it is absorbed by the first 1mm of human skin and was therefore not considered to be an issue, either detrimental of beneficial, deeper than this.

The team, from the Riken Center for Advanced Photonics, has shown that effects are felt deeper than this, and that terahertz radiation can disrupt proteins in living cells, without killing the cells. “This finding implies that terahertz radiation, which was long considered impractical to use, may have applications in manipulating cell functions for the treatment of cancer, for example, but also that there may be safety issues to consider,” according to the research institution.

It looks as though the mechanism for this deeper interaction could be the generation of mechanical shock-waves from instantaneous heating as the radiation is absorbed at the skin surface. Simple heating has been eliminated as a mechanism for deeper interaction as the temperature rise was only ~1.4°C.

Riken’s team looked at effects on the protein actin. It comes in two forms, with (G)-actin polymerising into long strands of (F)-actin. THz radiation slowed this change, leading to a to a decrease in filaments. To further test the hypothesis, they performed experiments in living cells, and found that in the cells as in the solution, the formation of actin filaments was disrupted. However, there was no sign that the radiation caused cells to die.

“It was quite interesting for us to see that terahertz radiation can have an effect on proteins inside cells without killing them cells themselves,” said Riken scientist Shota Yamazaki. “We will be interested in looking for potential applications in cancer and other diseases.”

A paper of the research, ‘Propagation of THz irradiation energy through aqueous layers: Demolition of actin filaments in living cells‘, has been published in Nature Scientific Reports. Available in full free, the clearly written paper begins with a brief survey of the known biological effects of THz radiation. Later it points out that similar shock-waves are already used in some medical applications, generated by infra-red or plasmas,