Spectroscopic Characterization and Differentiation of SARS-CoV-2 Virus-like Particles

Virus-like particles (VLPs) are recombinant, noninfectious, self-assembled structures that are made up of the viral structural proteins that mimic the morphology of viruses but lack genomic material. VLPs have been used to develop vaccines against viruses and cancer, leading to a surge of industry interest in exploring VLP vaccines. There are strict quality controls as a part of downstream processing in the production of nonreplicating VLPs. We characterized SARS-CoV-2 VLPs of the Beta and Omicron BA.5 subvariants, which differ in 43 amino acids in the spike protein. By comparing the Raman spectra of these particles with those of SARS-CoV-2 virions and purified RNA isolated from yeast, we confirmed the absence of genomic material in the VLPs, a crucial requirement for validating manufactured VLP vaccines. Principal component analysis (PCA) was applied to UV–visible spectra between 240 and 300 nm wavelength and Raman spectra in the range of 3200–800 cm^–1. The PCA score plots showed a clear separation between Beta and Omicron BA.5 VLPs. This study shows that spectroscopic techniques, combined with chemometric tools, can be used for rapid, label-free analysis with minimal sample preparation for the characterization of the VLPs. Thus, Raman spectroscopy can serve as a valuable tool for ensuring the structural integrity and quality control of VLPs for vaccine production.