Light-Induced Transformation of Virus-Like Particles on TiO2

Titanium dioxide (TiO2) shows significant potential as a self-cleaning material to inactivate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and prevent virus transmission. This study provides insights into the impact of UV-A light on the photocatalytic inactivation of adsorbed SARS-CoV-2 virus-like particles (VLPs) on a TiO2 surface at the molecular and atomic levels. X-ray photoelectron spectroscopy, combined with density functional theory calculations, reveals that spike proteins can adsorb on TiO2 predominantly via their amine and amide functional groups in their amino acids blocks. We employ atomic force microscopy and grazing-incidence small-angle X-ray scattering (GISAXS) to investigate the molecular-scale morphological changes during the inactivation of VLPs on TiO2 under light irradiation. Notably, in situ measurements reveal photoinduced morphological changes of VLPs, resulting in increased particle diameters. These results suggest that the denaturation of structural proteins induced by UV irradiation and oxidation of the virus structure through photocatalytic reactions can take place on the TiO2 surface. The in situ GISAXS measurements under an N2 atmosphere reveal that the virus morphology remains intact under UV light. This provides evidence that the presence of both oxygen and UV light is necessary to initiate photocatalytic reactions on the surface and subsequently inactivate the adsorbed viruses. The chemical insights into the virus inactivation process obtained in this study contribute significantly to the development of solid materials for the inactivation of enveloped viruses.


Preparation of TiO 2 (101)
The TiO 2 (101) single crystal (8 mm × 8 mm × 2 mm, Surface Net Ltd.) was prepared by 1.0 kV Ar + ion bombarated and 850 K anneal cycles in a backpack pressure of 1 ×10 −6 mbar of O 2 .This cleaning cycle was repeated until a sharp (1×1) low energy electron diffraction (LEED) pattern was obtained and XPS showed a clean surface free of contamination without any Ti 3+ defects (Figure S2 a, b).These measurements were carried out using XPS setup in the DESY Nanolab at the Centre for X-ray and Nano Science (CXNS). 1 After the experiment, the surface was cleaned in low concentrated acid solution and then we repeated the sputtering and annealing cycles.The sample was characterized by XPS.According to the XPS results of the reused sample, the Ti 2p core-level scan showed no Ti 3+ defects (Figure S2

X-ray Photoelectron Spectroscopy (XPS)
The core-level spectra for all samples are normalized to the intensity of Ti 2p   Table S2: CLSs calculated for different N species included in our adsorbed models.The isolated cysteine dipeptide is taken as the energy reference.

Figure
Figure S1: (a) Schematic structure of SARS-CoV-2 virus like particle (VLP) was generated by transfection of HEK293T cell with an optimized ratio of structural proteins S, M, N, and E in the presence of activator peptide (CD63 HiBiT).(b) Schematic view of SARS-CoV-2 virion.
c), and the O 1s spectrum clearly indicated the presence of lattice oxygen (Figure S2 d).

Figure
Figure S2: (a) LEED and XPS survey scan (b) of the clean anatase TiO 2 (101).The survey spectrum was recorded at a photon energy 1486.6 eV using a Al Kα source.(c, d) Ti 2p and O 1s core-level scans of the clean sample and reused sample after sputtering and annealing process.

Figure S5 :
Figure S5: Deconvoluted core-level photoelectron spectra of O 1s (a) and Ti 2p (b) of adsorbed VLPs on TiO 2 (101) surface.The measurements were performed at a photon energy 1.486 keV.

Figure S6 :
Figure S6: Sketch of isolated (a) cysteine and (b) asparagine monopeptides and (c) cysteine dimer.Different chemical species are highlighted by different colors; in the case of N groups, amino (blue) and amide (cyan) are further distinguished.

Figure
Figure S7: Horizontal and vertical cuts of beam damage scan.

Figure S8 :
Figure S8: Exemplary raw GISAXS detector image.Note the shadowed areas due to beam stops, evacuated flight tubes and inter-modular gaps, which are present due to the experimental setup beamline P03.

A
resolution : height of resolution function, w resolution : width of resolution function, S V LP : scale factor of VLP population, R V LP : Mean radius of VLP population, PDI V LP : Polydispersity index (PDI) of VLP population = σ V LP / R V LP , σ V LP : Gaussian standard deviation of radii of VLP population in Å, S surf ace−proteins : scale factor of Spike protein population, R surf ace−proteins : Mean radius of Spike protein population, PDI surf ace−proteins : Polydispersity index (PDI) of surface proteins population = σ surf ace−proteins / R surf ace−proteins , σ surf ace−proteins : Gaussian standard deviation of radii of surface proteins population in Å, S Byproduct : scale factor of viral byproducts population, R Byproduct : Mean radius of viral byproducts population, PDI Byproduct : Polydispersity index (PDI) of viral byproducts population = σ Byproducts / R Byproducts , σ Byproducts : Gaussian standard deviation of radii of viral byproducts population in Å.

Figure S9 :
Figure S9: Left: The horizontal line cuts at the region of interest in 2D GISAXS for clean TiO 2 (101) surface, adsorbed VLPs and after 30 min UV-A irradiation (Wavelength: 365 nm, Intensity: 850 µW/cm 2 ) under air (a) and N 2 atmosphere (b).Right: Experimental setup at the P03 beamline for the measurements under air and N 2 atmosphere.

Table S3 :
GISAXS data fitting parameters for adsorbed VLP on TiO 2 surface before and after UV irradiation.