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SARS-CoV-2 is the causative agent of COVID-19, which is a global pandemic. SARS-CoV-2 is transmitted rapidly via contaminated surfaces and aerosols, emphasizing the importance of environmental disinfection to block the spread of virus. Ultraviolet C radiation and chemical compounds are effective for SARS-CoV-2 disinfection, but can only be applied in the absence of humans due to their toxicities. Therefore, development of disinfectants that can be applied in working spaces without evacuating people is needed. Here we showed that TiO2-mediated photocatalytic reaction inactivates SARS-CoV-2 in a time-dependent manner and decreases its infectivity by 99.9% after 20 min and 120 min of treatment in aerosol and liquid, respectively. The mechanistic effects of TiO2 photocatalyst on SARS-CoV-2 virion included decreased total observed virion count, increased virion size, and reduced particle surface spike structure, as determined by transmission electron microscopy. Damage to viral proteins and genome was further confirmed by western blotting and RT-qPCR, respectively. The multi-antiviral effects of TiO2-mediated photocatalytic reaction implies universal disinfection potential for different infectious agents. Notably, TiO2 has no adverse effects on human health, and therefore, TiO2-induced photocatalytic reaction is suitable for disinfection of SARS-CoV-2 and other emerging infectious disease-causing agents in human habitation.

Febrile neutropenia (FN) is life-threatening condition, and airborne microorganisms have been identified as one of the potential transmission routes. The objective of this study was to evaluate spatial sterilization using photocatalytic oxidative decomposition reactions which are effective to prevent FN. An air purifier equipped with a platinum-added titanium dioxide photocatalytic and LED light source (LED-TiO2 device) was installed in hospital rooms (per 21.5–35 m3) to investigate changes in FN incidence and airborne microorganism counts. Airborne microorganisms in the hospital rooms matched those responsible for nosocomial infections. The incidence of FN was significantly reduced after installation of the LED-TiO 2 device [9/13 vs. 2/12, P-value (P) = 0.015]. The LED-TiO 2 device decreased the number of airborne microorganisms in patient-free rooms by approximately 75% after 2 h [P < 0.001]. When patient was in the room, the number of airborne microorganisms increased with medical procedure. However, after 20 min of procedure, the number of airborne microorganisms was approximately 50% lower than without the device room [P = 0.019]. The LED-TiO 2 device successfully achieved spatial disinfection of hospital rooms, and reduced the incidence of FN. Spatial disinfection using photocatalysts is considered an effective new infection prevention measure for patients with severe neutropenia undergoing cancer treatment.

Aerosols are a major transmission route for seasonal influenza infections. Titanium dioxide (TiO2) photocatalyst has broad-spectrum antiviral activity, including in vitro influenza virus inactivation; however, whether the TiO2 photocatalyst can effectively inactivate airborne influenza A viruses in vivo under conditions that mimic natural aerosol transmission remains unclear. Here, we evaluated in vivo inactivation of airborne H1N1 seasonal influenza virus by a photocatalyst-equipped air purifier using a mouse model. Influenza virus WSN strain aerosols were sprayed in a 60 L acrylic box with a nebulizer, circulated through a photocatalyst-equipped air purifier, exposed to BALB/c mice for 40 min after circulation, and subsequently collected with an air sampler. Thirty minutes of TiO2 photocatalyst treatment reduced influenza virus infectivity by 99.97%, and significantly lowered lung viral titer in mice on day 3 post-infection. Over 14 days post-infection, mice showed no >10% weight loss, 100% survival, and disease progression to the PBS (−) aerosol group. This suggests that the photocatalyst-equipped air purifier may reduce H1N1 seasonal influenza onset, preventing viral spread.

The highly pathogenic avian influenza virus (HPAIV) is widely distributed worldwide and causes significant economic losses. Transmission of HPAIV occurs through direct contact between infected and susceptible birds or indirectly via contaminated materials. In recent years, airborne transmission of HPAIV has also been reported, underscoring the need for novel approaches to effectively inactivate airborne HPAIV. Photocatalysts have attracted significant attention as potential antiviral agents. In this study, we demonstrated that a TiO2-mediated photocatalytic reaction inactivated HPAIV and H1N1 seasonal influenza viruses in liquid, reducing their infectivity by 90.7% and 94.4%, respectively, after 60 min. Mechanistic analyses revealed decreased virion size and surface structure disruption, as determined by transmission electron microscopy. Additional evidence of viral protein and genome damage was obtained using Western blotting and RT-qPCR, respectively. Given the broad antiviral activity of photocatalysts, these findings suggest that they can inactivate influenza viruses regardless of strain or subtype. Notably, photocatalysts inactivated 80% of aerosolized H1N1 seasonal influenza viruses within 5 min. These results provide strong evidence that photocatalysts are capable of inactivating airborne influenza viruses. This study represents the first demonstration that photocatalysts can inactivate HPAIV and aerosolized influenza viruses. These findings provide strong evidence that photocatalysts represent a promising countermeasure against HPAIV, with potential applicability across different strains and subtypes.

Legionella pneumophila (L. pneumophila) is the causative agent of Legionnaires’ disease and Pontiac fever, collectively known as legionellosis. L. pneumophila infection occurs through inhalation of contaminated aerosols from water systems in workplaces and institutions. The development of disinfectants that can eliminate L. pneumophila in such water systems without evacuating people is needed to prevent the spread of L. pneumophila. Photocatalysts are attractive disinfectants that do not harm human health. In particular, the TiO2 photocatalyst kills L. pneumophila under various conditions, but its mode of action is unknown. Here, we confirmed the high performance of TiO2 photocatalyst containing PtO2 via the degradation of methylene blue (half-value period: 19.2 min) and bactericidal activity against Escherichia coli (half-value period: 15.1 min) in water. Using transmission electron microscopy, we demonstrate that the disinfection of L. pneumophila (half-value period: 6.7 min) by TiO2 photocatalyst in water is accompanied by remarkable cellular membrane and internal damage to L. pneumophila. Assays with limulus amebocyte lysate and silver staining showed the release of endotoxin from L. pneumophila due to membrane damage and photocatalytic degradation of this endotoxin. This is the first study to demonstrate the disinfection mechanisms of TiO2 photocatalyst, namely, via morphological changes and membrane damage of L. pneumophila. Our results suggest that TiO2 photocatalyst might be effective in controlling the spread of L. pneumophila.

Allergies to dogs and cats can cause enormous damage to human health and the economy. Dog and cat allergens are mainly found in dog and cat dander and are present in small particles in the air and in carpets in homes with dogs and cats. Cleaning houses and washing pets are the main methods for reducing allergens in homes; however, it is difficult to eliminate them completely. Therefore, we aimed to investigate whether a TiO2 photocatalyst could degrade dog and cat allergens. Under wet conditions, exposure to the TiO2 photocatalyst for 24 h degraded Can f1, which is a major dog allergen extracted from dog dander, by 98.3%, and Fel d1, which is a major cat allergen extracted from cat dander, by 93.6–94.4%. Furthermore, under dry conditions, the TiO2 photocatalyst degraded Can f1 and Fel d1 by 92.8% and 59.2–68.4%, respectively. The TiO2 photocatalyst abolished the binding of dog and cat allergens to human IgE by 104.6% and 108.6%, respectively. The results indicated that the TiO2 photocatalyst degraded dog and cat allergens, causing a loss in their allergenicity. Our results suggest that TiO2 photocatalysis can be useful for removing indoor pet allergens and improving the partnership between humans and pets.

The highly pathogenic avian influenza virus (HPAIV) is widely distributed worldwide and causes significant economic losses. Transmission of HPAIV occurs through direct contact between infected and susceptible birds or indirectly via contaminated materials. In recent years, airborne transmission of HPAIV has also been reported, underscoring the need for novel approaches to effectively inactivate airborne HPAIV. Photocatalysts have attracted significant attention as potential antiviral agents. In this study, we demonstrated that a TiO[sub.2]-mediated photocatalytic reaction inactivated HPAIV and H1N1 seasonal influenza viruses in liquid, reducing their infectivity by 90.7% and 94.4%, respectively, after 60 min. Mechanistic analyses revealed decreased virion size and surface structure disruption, as determined by transmission electron microscopy. Additional evidence of viral protein and genome damage was obtained using Western blotting and RT-qPCR, respectively. Given the broad antiviral activity of photocatalysts, these findings suggest that they can inactivate influenza viruses regardless of strain or subtype. Notably, photocatalysts inactivated 80% of aerosolized H1N1 seasonal influenza viruses within 5 min. These results provide strong evidence that photocatalysts are capable of inactivating airborne influenza viruses. This study represents the first demonstration that photocatalysts can inactivate HPAIV and aerosolized influenza viruses. These findings provide strong evidence that photocatalysts represent a promising countermeasure against HPAIV, with potential applicability across different strains and subtypes.

Legionella pneumophila (L. pneumophila) is the causative agent of Legionnaires’ disease and Pontiac fever, collectively known as legionellosis. L. pneumophila infection occurs through inhalation of contaminated aerosols from water systems in workplaces and institutions. The development of disinfectants that can eliminate L. pneumophila in such water systems without evacuating people is needed to prevent the spread of L. pneumophila. Photocatalysts are attractive disinfectants that do not harm human health. In particular, the TiO[sub.2] photocatalyst kills L. pneumophila under various conditions, but its mode of action is unknown. Here, we confirmed the high performance of TiO[sub.2] photocatalyst containing PtO[sub.2] via the degradation of methylene blue (half-value period: 19.2 min) and bactericidal activity against Escherichia coli (half-value period: 15.1 min) in water. Using transmission electron microscopy, we demonstrate that the disinfection of L. pneumophila (half-value period: 6.7 min) by TiO[sub.2] photocatalyst in water is accompanied by remarkable cellular membrane and internal damage to L. pneumophila. Assays with limulus amebocyte lysate and silver staining showed the release of endotoxin from L. pneumophila due to membrane damage and photocatalytic degradation of this endotoxin. This is the first study to demonstrate the disinfection mechanisms of TiO[sub.2] photocatalyst, namely, via morphological changes and membrane damage of L. pneumophila. Our results suggest that TiO[sub.2] photocatalyst might be effective in controlling the spread of L. pneumophila.

Allergies to dogs and cats can cause enormous damage to human health and the economy. Dog and cat allergens are mainly found in dog and cat dander and are present in small particles in the air and in carpets in homes with dogs and cats. Cleaning houses and washing pets are the main methods for reducing allergens in homes; however, it is difficult to eliminate them completely. Therefore, we aimed to investigate whether a TiO[sub.2] photocatalyst could degrade dog and cat allergens. Under wet conditions, exposure to the TiO[sub.2] photocatalyst for 24 h degraded Can f1, which is a major dog allergen extracted from dog dander, by 98.3%, and Fel d1, which is a major cat allergen extracted from cat dander, by 93.6–94.4%. Furthermore, under dry conditions, the TiO[sub.2] photocatalyst degraded Can f1 and Fel d1 by 92.8% and 59.2–68.4%, respectively. The TiO[sub.2] photocatalyst abolished the binding of dog and cat allergens to human IgE by 104.6% and 108.6%, respectively. The results indicated that the TiO[sub.2] photocatalyst degraded dog and cat allergens, causing a loss in their allergenicity. Our results suggest that TiO[sub.2] photocatalysis can be useful for removing indoor pet allergens and improving the partnership between humans and pets.

SARS-CoV-2 is the causative agent of COVID-19, which is a global pandemic. SARS-CoV-2 is transmitted rapidly via contaminated surfaces and aerosols, emphasizing the importance of environmental disinfection to block the spread of virus. Ultraviolet C radiation and chemical compounds are effective for SARS-CoV-2 disinfection, but can only be applied in the absence of humans due to their toxicities. Therefore, development of disinfectants that can be applied in working spaces without evacuating people is needed. Here we showed that TiO -mediated photocatalytic reaction inactivates SARS-CoV-2 in a time-dependent manner and decreases its infectivity by 99.9% after 20 min and 120 min of treatment in aerosol and liquid, respectively. The mechanistic effects of TiO photocatalyst on SARS-CoV-2 virion included decreased total observed virion count, increased virion size, and reduced particle surface spike structure, as determined by transmission electron microscopy. Damage to viral proteins and genome was further confirmed by western blotting and RT-qPCR, respectively. The multi-antiviral effects of TiO -mediated photocatalytic reaction implies universal disinfection potential for different infectious agents. Notably, TiO has no adverse effects on human health, and therefore, TiO -induced photocatalytic reaction is suitable for disinfection of SARS-CoV-2 and other emerging infectious disease-causing agents in human habitation.