Analysis of the SARS-CoV-2 inactivation mechanism using violet-blue light (405 nm)

The COVID-19 pandemic has highlighted the urgent need for efficient and sustainable disinfection solutions that can reduce the spread of airborne and surface infections. Light-based disinfection technologies have attracted significant interest due to their non-invasive properties, adaptability and environmental benefits. Violet-blue light (VBL) at 405 nm has been shown to be an effective method, inducing the production of reactive oxygen species (ROS) that reduce microbial viability. This work aims to clarify the inactivation processes of SARS-CoV-2 during VBL exposure, thereby aiding the development of novel antiviral methods. The study assessed the effects of VBL on cell viability, replication, carbonylation of 3 structural proteins (spike (S), envelope (E) and nucleoprotein (N)) and 1 non-structural protein (NSP13 helicase), and direct damage to viral RNA. SARS-CoV-2 was exposed to increasing doses of VBL along with influenza A and B viruses to assess susceptibility to VBL compared to other airborne RNA viruses. At the higher dose, SARS-CoV-2 was significantly more susceptible to VBL compared to influenza viruses, with 2.33 log10 viral titer reduction after 90’ exposure at 21.6 J/cm2. Viral RNA after exposure to VBL showed no significant changes as assessed by NGS and qRT-PCR, suggesting that the inactivation process does not involve direct nucleic acid damage. Cell viability experiments were performed using different dilutions of DMEM medium in PBS (1:3, 1:20 and 1:1,000) to exclude the responsibility of the culture suspension in the inactivation process. The results indicated that the suspension medium played a minor role in virus inactivation, as viability did not increase with increasing dilution of DMEM. Subsequent tests with three different antioxidants (NAC, AsA and SOD) at different concentrations contributed to counteract the oxidative process and increase viability up to a maximum of 14.33% (with SOD 0.003 mM). Carbonylation of S and E protein was more pronounced when viruses were suspended in DMEM medium containing photosensitive molecules, although tests showed that the intrinsic properties of the viral membrane were a crucial element to consider in relation to its susceptibility to VBL. Indeed, lipid peroxidation has been identified as an important factor affecting the structural integrity and function of the viral envelope, impairing the ability of the virus to interact with host cells and leading to non-infectivity. The SARS-CoV-2 envelope lipidomic, composed predominantly of glycerophospholipids and devoid of cholesterol and sphingolipids, appears to be the critical factor in its susceptibility, distinguishing it from influenza viruses, which have a lipid profile richer in protective components against oxidative stress. The results highlight the efficacy of VBL as a non-invasive disinfection method for use in healthcare, public areas and air filtration systems. In contrast to conventional UV disinfection techniques, VBL operates at safer wavelengths, reducing the risks associated with exposure. This makes it a particularly attractive choice for environments that require regular and safe disinfection. In conclusion, VBL offers a realistic option for viral inactivation, particularly against SARS-CoV-2. Further research should improve VBL procedures, investigate its synergistic interactions with other disinfection techniques, and evaluate its efficacy in practical applications to facilitate its use as a novel and efficient disinfection approach.