Surprising effect: Terahertz radiation, which is considered to be harmless, could have an effect on cells and tissues, as an experiment suggests. Accordingly, this radiation does not penetrate the skin or other tissues, but its energy does. And this can obviously damage cellular proteins such as the actin filaments. Even if the cells survived despite this damage, this biological effect should be examined in more detail, according to the researchers in the scientific journal “Scientific Reports”.
The terahertz radiation between infrared and microwaves can penetrate many common materials such as paper, textiles or plastic without destruction. It is therefore used for material tests, but also for security checks at the airport. So far, it has been a great advantage that, in contrast to short-wave X-rays, this radiation does not damage the cells or the DNA.
Shock wave damage?
But that could only be partially true, as researchers around Shota Yamazaki from the RIKEN research center in Sendai have now determined. The terahertz radiation is already completely absorbed on the surface of the skin and therefore penetrates as far as possible into the top cell layer. “But if the terahertz radiation is converted into a form of energy that can penetrate further, it could still cause damage inside the tissues,” the researchers explain.
In previous experiments, they had already observed that terahertz radiation in water can generate shock waves that penetrate several millimeters deep. In order to find out whether these shock waves can also damage cell components, the researchers have now exposed biological cell components to pulses of terahertz radiation. As the first test object, they chose a solution of actin filaments. These protein threads form the cell structure and are an important part of the muscle fibers.
Destroyed actin filaments
When the researchers irradiated the actin dissolved in water with terahertz pulses of 80 microjoules per square centimeter, there was an effect: while the actin filaments in the control solution remained intact, their amount in the irradiated sample decreased by 50 percent, as Yamazaki and his colleagues report. This reduction suggests that the radiation disrupted the formation of these filaments.
However, the terahertz radiation itself cannot be responsible for this. “The high absorption effect of the water limits the depth of penetration to around ten micrometers – this corresponds to only around one percent of the sample volume,” said the researchers. Because the sample hardly heated up, they suspect that the radiation was converted into mechanical energy, which then caused the actin filaments to decay.
“Our results demonstrate that the energy of terahertz radiation can penetrate more than a millimeter into an aqueous solution,” the scientists state. “The radiation energy is apparently converted into a pressure wave, which can then destroy cellular actin filaments.”
Damage also in living cells
But what is the effect on living cells? To test this, the scientists now exposed a cell culture to the terahertz pulses. The cells were placed in the nutrient medium so that there was a distance of 800 to 1,800 microns between them and the surface. A direct radiation effect was excluded.
This experiment also showed damage after radiation: “The actin filaments were reduced and clumped actin complexes were observed at the cell edge,” report Yamazaki and his colleagues. A comparison with a control culture showed that the temperature of the batches only differed by 0.5 degrees – excessive heating due to the radiation was therefore not the reason for this damage.
After all, the researchers were unable to observe any extensive damage to the cells. Terahertz radiation also appeared to have no negative effect on cell survival. “It is interesting that terahertz radiation can act on the cellular proteins without killing the cells,” says Yamazaki.
Further studies advisable
According to the scientists, these new findings should also be taken into account in future applications of terahertz technology. “It is important to fully understand the effect of this radiation on biological tissue – both to assess the risks and to use this effect for possible applications,” explains Chiko Otani from the RIKEN research center.
Further studies on these effects are therefore sensible and necessary, the scientists emphasize. Nevertheless: If you go through the terahertz scanner at the airport, you probably don’t have to worry. Because this effect hits the top millimeter of the skin at most – and whether it occurs at all in this form of application is completely open. (Scientific Reports, 2020; doi: 10.1038 / s41598-020-65955-5)
Source: RIKEN
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