PRESS RELEASE
Source:Nara Medical UniversityKanagawa Institute of Industrial Science and Technology
Tokyo Institute of Technology
For immediate release: April 14, 2022

Scientists Develop Indoor-active Photocatalyst for Antiviral Coating Against VariousVariant Types of Novel Coronavirus SARS-CoV-2(Japan, April 14) Photocatalyst made using a combination of titanium dioxide (TiO2) andcopper oxide (CuxO) nanoclusters inactivates various variant types of novel coronavirus
SARS-CoV-2. Scientists in Nara Medical University, Kanagawa Institute of Industrial Scienceand Technology, and Tokyo Institute of Technology have developed this antiviralphotocatalyst, in a recent breakthrough, which has been proven to be effective under bothdarkness and indoor light.
Highlights✓ CuxO/TiO2 inactivates various variant types (Alfa, Beta, Gamma, and Delta) of SARS-CoV2 below their detection limit for 2 h under visible light irradiation (Figure 1).
✓ CuxO/TiO2 also exhibits the antiviral activity even under dark conditions.
✓ Antiviral activity on CuxO/TiO2 is caused by denaturation of spike proteins and RNA
fragmentation of SARS-CoV-2 viruses.
1.E+07107①②virus titer (PFU/mL)

1.E+06106glass under dark
系列2glass under visible light
系列1
CuxO/TiO2 under dark
系列3
CuxO/TiO2 under visible light
系列4

1.E+05105
1.E+04104
1.E+03103
1.E+02
102**

23① SARS-CoV-2-virus (white spots)
observed on a plain glass substrate.
② No white spots observed on theCuxO/TiO2 coated substrate.

* detection limit

1.E+01100

1Time (hour)
Figure 1: Antiviral effect towards Delta valiant of SARS-CoV-2 by the photocatalyst coating under light anddark conditions
The TiO2/CuxO coating inactivates viruses even under dark condition. Its antiviral activity is further enhanced byvisible light irradiation.

Image credit: Ryuichi Nakano from Nara Medical University

The novel coronavirus (SARS-CoV-2), responsible for the ongoing COVID-19 pandemic, hasaffected millions of people worldwide. The main transmission pathway of the virus is throughdroplets released by infected people into the air. Additionally, these droplets exist on various
surfaces as well. Viral infections mainly occur in indoor environments where many people
gather, Antiviral chemicals, such as alcohol and hydrogen peroxide, are often used todecontaminate regularly touched surfaces. These chemicals essentially render the virus
inactive by breaking down their proteins. However, these chemicals are volatile in nature and,
therefore evaporate away. As a result, the disinfection process has to be carried out regularly.
Now in a study published in Scientific Reports, a research team of Nara Medical University,
Kanagawa Institute of Industrial Science and Technology, and Tokyo Institute of Technology
has developed a solid-state photocatalyst as an alternative defense against the virus. Unlikechemical disinfectants, solid-state coatings remain for a long time, and since the viraloutbreak, have been the subject of intensive research around the world. Solid-state antiviralcoatings have the advantage of being non-toxic, abundant, and chemically and thermallystable.
Many of these solid-state coatings use TiO2 photocatalysts that, when exposed to ultraviolet(UV) light, cause oxidation reaction that can destroy organic matter like the spike proteinsfound on the surfaces of coronaviruses. However, these coatings are activated only when
exposed to UV light, which is not present in typical indoor environments. In most of indoor
environments, lightings are usually turned off in the night time, thus the antiviral material
under dark condition is desired.
To get the coating to work under visible light as well dark conditions, the team has developed
a composite consisting of TiO2 and CuxO nanoclusters (Figure 2). CuxO nanoclusters arecomposed of a mixed valence number oxide, in which Cu(I) and Cu(II) species are present. TheCu(II) species in CuxO contributes to the visible-light-driven photocatalysis reaction, whereasthe Cu(I) species plays a crucial role in denaturing virus proteins, thereby causing theirinactivation under dark conditions.

CuxO

TiO250 nm

Figure 2. TEM image of copper oxide/titanium oxide composite (CuxO/TiO2)
Small CuxO nanoclasters are grafted on TiO2 particles.
Image credit: Masahiro Miyauchi from Tokyo Institute of Technology

By coating the CuxO/TiO2 powder on a glass, the team showed that it could inactivate eventhe highly virulent Delta variant of SARS-CoV-2 as shown in Figure 1. The team has also
confirmed the inactivation of Alfa, Beta, and Gamma variants by CuxO/TiO2 in addition to thewild type strain.
The team carefully investigated the antiviral mechanism using sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE), ELISA assay, and RT-qPCR analysis. Theseanalyses strongly suggest that the Cu(I) species in CuxO denaturalises spike proteins and also
causes RNA fragmentation of SARS-CoV-2, even under dark condition (Figure 3). Furthermore,white light irradiation causes the photocatalytic oxidation of the organic molecules of SARSCoV-2. Based on this antiviral mechanism, the present antiviral material is not limited to a
specific variant of the virus and will be effective to inactivate various types of a potential
mutant strain.

SARS-CoV-2
spike protein

Both spike proteins andRNAs were damaged.

photocatalytic oxidation

RNA

CuxO/TiO2
substrate
Figure 3. The proposed antiviral mechanism of the photocatalyst coating
The TiO2/CuxO coating inactivates the virus by fragmenting and oxidizing spike proteins and RNAs of SARS-CoV2.
Image credit: Ryuichi Nakano from Nara Medical University

White light illumination in the present study is usually used as an indoor light apparatus. Thiscan make the CuxO/TiO2 photocatalyst very effective in reducing the risk of COVID-19
infection in indoor environments, which are usually subjected to both light and darkness
periodically.
Hopefully, this study will take us one step closer to protecting ourselves better against thecoronavirus, and adjusting to the post-COVID era.

Reference
Authors:

Title of original paper:
Journal:DOI:
Affiliations:

Ryuichi Nakano 1*, Akira Yamaguchi 2, Kayano Sunada 3, Takeshi Nagai 3,Akiyo Nakano 1, Yuki Suzuki 1, Hisakazu Yano 1, Hitoshi Ishiguro 3*, andMasahiro Miyauchi 2*
Inactivation of Various Variant Types of SARS-CoV-2 by Indoor-lightsensitive TiO2-based Photocatalyst
Scientific Reports
10.1038/s41598-022-09402-7
1
Nara Medical University, Japan
2
Tokyo Institute of Technology, Japan
3
Kanagawa Institute of Industrial Science and Technology, Japan*Corresponding authors’ emails: rnakano@naramed-u.ac.jp (R.N.), pgishiguro@newkast.or.jp(H.I.), mmiyauchi@ceram.titech.ac.jp(M.M.)
Contacts
Masaki Sakata
Nara Medical University
sangaku@naramed-u.ac.jp
Research and Development Department,
Kanagawa Institute of Industrial Science and Technology
rep-kenkyu@kistec.jp
Emiko Kawaguchi
Public Relations Division,
Tokyo Institute of Technology
media@jim.titech.ac.jp+81-3-5734-2975

About Nara Medical University
A prefectural medical vocational school was established in Nara in April 1945 and wastransformed into the predecessor of Nara Medical University in 1948. It was thenreorganized into the present Nara Medical University in 1952. Nara Medical University
College of Nursing was established in 1996, and it was re-organized as the Faculty ofNursing, School of Medicine, Nara Medical University in 2004. Since then, Nara MedicalUniversity has been steadily advancing as a medical university with the Faculty of Medicine
and the Faculty of Nursing, School of Medicine.
https://www.naramed-u.ac.jp/university/english/
About Kanagawa Institute of Industrial Science and Technology
Kanagawa Institute of Industrial Science and Technology (“KISTEC”) is a local incorporated
administrative agency established in April 2017. KISTEC has been founded by merger of public
test and research institute Kanagawa Industrial Technology Center ("KITC") and public interest

incorporated foundation Kanagawa Academy of Science and Technology ("KAST"). We
promote regional industry and science and technology, utilizing the mutual advantages ofKITC’s technical support capability and KAST’s research and development capability. And wealso try to make the residents’ lives more enriched, and to fulfill the needs of our users, withfive main activities; “Research and Development”, “Technical Support”, “Commercialization
Support”, “Personnel Training”, and “Collaborative Network”.
About Tokyo Institute of Technology
Tokyo Tech stands at the forefront of research and higher education as the leading university
for science and technology in Japan. Tokyo Tech researchers excel in fields ranging frommaterials science to biology, computer science, and physics. Founded in 1881, Tokyo Techhosts over 10,000 undergraduate and graduate students per year, who develop into scientificleaders and some of the most sought-after engineers in industry. Embodying the Japanesephilosophy of “monotsukuri,” meaning “technical ingenuity and innovation,” the Tokyo Techcommunity strives to contribute to society through high-impact research.
https://www.titech.ac.jp/english/