Researchers find cheap, easy way to disinfect N95 masks

Despite the distribution of a COVID-19 vaccine “we know there is still a huge demand for PPE." 

Media Contact: Barbara Clements,, 253-740-5043

A small amount of methylene blue, with a large dose of sunlight or bright light, is all that’s needed to inactivate the coronavirus on N95 masks. These are  the gold standard for masks among health-care workers.  This method also works  on some other personal protection equipment, or PPE, so needed by medical workers, a new study released December 11 concluded.

The findings were part of a 6-month-long DeMaND study (Development of Methods for Mask and N95 Decontamination), which involves researchers from the Centers for Disease Control and Prevention, from the World Health Organization, and from 12 institutions, including the University of Washington School of Medicine and Seattle Children’s Research Institute.

 “This is a valuable tool to health-care workers in low or medium-income countries, who don’t have access to either refrigeration or highly technical means of sterilization,” said Dr. Thomas Lendvay,  lead author of the study. Lendvay is a UW Medicine urologist and also a pediatric urologist with Seattle Children’s Hospital.

For the past ten months, Lendvay and Dr. Tanner Clark have worked with Dr. James Chen, a Seattle neurosurgeon, examining the viability of disinfecting N95 masks so that health-care workers can reuse them safely. Infectious diseases specialist Dr. Jaya Sahni and HIV researcher, Dr. Thor Wagner, of the Seattle Children’s Research Institute. also became collaborators after Wagner’s lab switched from studying HIV to COVID-19 after the pandemic emerged this spring.

Despite the advent of a COVID-19 vaccine, which began distribution to frontline health-care workers in Washington state Dec.  15,  “we know there is still a huge demand for PPE and masks during this pandemic. They are all still of limited supply and now we are being asked to reuse these masks and gear,” Lendvay said.

In addition, Lendvay noted, droplets on the gear can potentially infect the wearer of the PPE as it’s taken off, because it’s been shown the virus can remain alive for hours on a mask.

Industry-standard masks, including the N95, are designed as single-use devices. It is very difficult to sanitize them without destroying them or rendering them toxic to the wearer. Currently a few commercially available products and methods effectively disinfect PPE, but most require expensive equipment that many hospitals cannot afford or manage.

Methylene blue is a readily available chemical, even in developing countries. It is used in the sterilization of blood plasma for transfusion and is also a topical sanitizer once it encounters light or sunlight.

What excited the researchers even more was the finding that once the methylene blue, the solution, is exposed to bright light, it continues to inactivate the coronavirus days after treating the mask material. It’s possible that health-care personnel could be protected for up to a week with a single mask treated with methylene blue used with standard indoor lighting.

In this research, three types of N95 masks were used (including the common 3M N95 1860 respirator, the teal colored half dome shaped ones we see so many nurses and frontline hospital workers wearing). The masks treated with 10 micromolar concentration of methylene blue were exposed to 50,000 lux of broad spectrum light or 12,500 lux of red light for 30 minutes. That’s the equivalent of taking 6-8 drops of the same 1% solution of methylene blue one can find on online shopping sites and mixing it in one liter of water. Another test, using dry heat of 75 degrees Celsius for one hour, was also employed. Both methods inactivated the virus.

Aside from the COVID-19 virus, the method was tested on two other types of coronavirus: the murine hepatitis virus and the porcine respiratory coronavirus.

The technology itself is not new, Lendvay said. The use of methylene blue and light was first used 90 years ago to treat mouth sores caused by viruses. Methylene blue was actually first invented in 1876 as textile dye. More recently this combination has been used to sterilize blood plasma before transfusions. Surgeons are familiar with it for identifying cancerous lymph nodes, and urologists use it to identify urinary tract structures.

Studies are underway to expand the use of methylene blue and light to decontaminate other PPE articles like gloves, gowns, eye protection, and for potential environmental applications.

The idea spawned from Chen, who used light activated dyes as part of brain cancer treatments. He approached Lendvay and the two started identifying applications for this technology, including how it could be used to address the risk of the pandemic to health-care personnel. Lendvay reached out to a former colleague at the CDC and eventually the idea was presented to a panel of WHO.

Lendvay and Chen have several ideas for how to get this technology into the hands of many and to do that, they have spun-out a company from the University of Washington’s CoMotion technology transfer center called Singletto, Inc. Representatives from the company are speaking with major PPE manufacturers to help improve existing PPE and develop novel applications that can help millions avoid getting infected.

The study paper is available on MedRxiv, a website where researchers can post pre-publication versions of their studies for discussion. Such posts, called pre-prints, have not yet undergone peer review nor been published in a scientific journal.

This research was conducted by a consortium of 52 researchers and scientists from around the world, in partnership with 13 organizations, universities, and laboratories, including the WHO, CDC and the British Standards Institution. This study was funded by Open Philanthropy; Amazon Inc./University of Washington Catalyst Award; University of Liege, Belgium, and the Walloon Region, Belgium; Li Ka Shing Institute; Alberta Health Services; and an anonymous donor to the University of Washington, Department of Urology. Authors Lendvay and Chen are co-founders and equity owners of Singletto, Inc., Seattle.  Authors Yi Cui and Steven Chu are co-founders and equity owners of 4C Air, Inc., Sunnyvale, Calif.

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