The second life for unused COVID-19 vaccines: Towards biosensing application

Many vaccines have been produced during the COVID-19 pandemic. Currently, an increasing number of vaccines have reached an expiration date without being used. Therefore, expired vaccines (EXVAX) based on virus-like particles (VLP) recombinant SARS-CoV2-S protein can be repurposed for biosensing application and provide a use, even though they are past their expiration date for vaccination. In the current study, we applied EXVAX based on VLP for gold sensor chip modification to use such surface for specific antibody detection from diluted human serum. For this purpose, we used total internal reflection ellipsometry for real-time kinetics measurement and mathematical modelling for the calculation of affinity constants. Moreover, we cross-validated the results obtained with a widely applied ELISA method. EXVAX was tested and compared with commercially available recombinant S proteins analogues that are commonly used for immunosensing. The results suggest that the EXVAX functionalisation is thermodynamically favoured. The interaction analysis of polyclonal antibodies from human serums shows that the EXVAX SARS-CoV2-S proteins retain their biological activity more than one year after the expiration date as the calculated values of the affinity constant fall in a nM range of (10^-11 > K_D > 10^-9), suggesting a high affinity interaction and thus could be used for biosensing and meet sustainable development goal.