Professor Yoshiyama succeeds in demonstrating that the novel coronavirus (variant strain included) contained in adherent saliva can be reduced through the use of Sharp's Plasmacluster technology.

公開日 2021/09/15



The News:

Professor Hironori Yoshiyama of the Department of Microbiology at Shimane University Faculty of Medicine (also board member of the Japanese Society for Virology) has demonstrated, under joint supervision with Professor Shigeru Watanabe of Meikai University School of Health Sciences, and Professor Masashi Yamakawa of the Department of Mechanical and System Engineering at Kyoto Institute of Technology, in collaboration with Sharp Corporation, that through exposure to Plasmacluster ions over a period of two hours in an environment of 60% humidity (the recommended condition for countering viral infection), the infectious titer of a novel coronavirus contained in adherent saliva can be reduced by more than 99.4%. This discovery is a world-first*.

*Ion-emission air purification technologies (as of July 15, 2021; based on Sharp research).


The Outline:

In general, the route of infection is thought to be broadly divided into droplet infection by airborne viral particles and contact infection by adherent viral particles. Sharp Corporation had demonstrated the effectiveness of Plasmacluster technology in reducing airborne coronavirus in September of 2020. This time, they have newly demonstrated its effect in reducing its adherent form.



  1. Simulating a real-life environment in which a person coughs in an environment of 30% versus 60% humidity, it was found that while fewer droplet particles were suspended in the air in a 60% humidity environment, they fell down and adhered to the table. Based on this result, it was thought important to also verify the effect of reducing the amount of adherent viral particles in an environment of 60% humidity.
  2. Since most of the droplets that cause the viral infection are derived from saliva, the infectious titer of environments of 60% humidity, one in which the viral particles were mixed with a liquid medium commonly used for virus testing, and another in which the viral particles were mixed with saliva, were measured and compared. The result showed that while the infectious titer remaining in the liquid medium after two hours was less than 1%, that of the saliva was 56%.

Test Results:

From these verification test results, assuming that the virus is present in adherent saliva in a real-life environment with 60% humidity, the effect of Plasmacluster technology was verified, and it was confirmed that the infectious titer was reduced by more than 99.4% (99.7% for the conventional strain and 99.4% for the variant strain).

  Comments from Professor Yoshiyama, Microbiology Dept., Shimane University

Maintaining the environment at a relative humidity of 60% is effective for protection against infection as this level of humidity prevents the human respiratory tract from drying out, thereby suppressing the infectivity of the virus. However, while airborne viral particles can be reduced in this environment, they fall down and adhere to surfaces. Countermeasures for these adhering viruses are also necessary. Adding on to last year’s discovery, to demonstrate that Plasmacluster technology inactivates the coronavirus contained in adherent saliva in an environment of 60% humidity while maintaining physiological protective function is significant. Furthermore, that this result also applies to the variant strain suggests that the same effect of reduction can be expected against new variants of the future.


[Inquiry] Department of Microbiology