Inactivation and spike protein denaturation of novel coronavirus variants by CuxO/TiO2 nano-photocatalysts

Abstract

In order to reduce infection risk of novel coronavirus (SARS-CoV-2), we developed nano-photocatalysts with nanoscale rutile TiO₂ (4-8 nm) and Cu_xO (1-2 nm or less). Their extraordinarily small size leads to high dispersity and good optical transparency, besides large active surface area. Those photocatalysts can be applied to white and translucent latex paints. Although Cu₂O clusters involved in the paint coating undergo gradual aerobic oxidation in the dark, the oxidized clusters are re-reduced under > 380 nm light. The paint coating inactivated the original and alpha variant of novel coronavirus under irradiation with fluorescent light for 3 h. The photocatalysts greatly suppressed binding ability of the receptor binding domain (RBD) of coronavirus (the original, alpha and delta variants) spike protein to the receptor of human cells. The coating also exhibited antivirus effects on influenza A virus, feline calicivirus, bacteriophage Qβ and bacteriophage M13. The photocatalysts would be applied to practical coatings and lower the risk of coronavirus infection via solid surfaces.

Figure 1

Colour and spectral changes of the photocatalysts. (a, c) Colour changes of the (a) rutile- and (c) anatase-based photocatalyst suspensions after leaving in the dark and under irradiation with simulated solar light. (b) Spectra of the as-prepared photocatalyst suspensions. (d–g) Photographs of the (d, f) rutile- and (e, g) anatase-based photocatalyst coating (d, e) with or (f, g) without white pigments. (h) Spectral changes of the rutile- and anatase-based coatings in the dark and under illumination (fluorescent light, > 380 nm, 500 lx).

Figure 2

Photocatalyst nanoparticles. (a–d) HAADF-STEM images of the photocatalysts. (e, f) STEM-EDS elemental mapping images for (e) Ti and (f) Cu.

Figure 3

Photoinduced chemical processes involved in the present photo-renewable system. (A) Aerobic oxidation of Cu(I) to Cu(II). (B) Photo-induced interfacial charge transfer from the TiO₂ VB to Cu(II). (C) Photo-excitation of electrons in the TiO₂ VB to CB. (D) Plasmonic excitation of over-reduced, metallic Cu nanoparticles, which inject electrons to the TiO₂ CB. Process B is the major photo-process and Processes C and D are minor processes.

Figure 4

Antivirus effects of the photocatalyst coatings on novel coronaviruses. Viral infectivity (V) values for (a) the original and (b) alpha variants of novel coronavirus after incubation under fluorescent light (1000 lx for 3 h) are shown. Raw data are summarized in Table S1 in Supplementary Information.

Figure 5

Antivirus effects of the photocatalyst coatings on bacteriophages. Viral infectivity (V) values for bacteriophage Qβ (a) after incubation under fluorescent light (500 lx for 4 h) or (b) in the dark and (c) those for bacteriophage M13 after incubation under fluorescent light (500 lx for 24 h) are shown. Raw data are summarized in Table S1 in Supplementary Information.

Figure 6

Denaturation effect of the rutile- and anatase-based photocatalysts on RBD domain of spike protein from (a) the original, (b) alpha and (c) delta variants of novel coronavirus. The binding activity of RBD to human ACE2 protein at various concentrations was assessed by ELISA (n = 3). Raw data are summarized in Table S2 in Supplementary Information.