The Gold Nanoparticles-Functionalized with the Synthetic PADRE^S2P6 Peptide Can Be Useful for SARS-CoV-2 Detection

Conjugation of bioactive peptides to nanomaterials is a promising approach for a variety of biomedical uses. Indeed, we assumed that gold nanoparticles (AuNPs) functionalized with synthetic viral peptides represent a promising strategy to elicit antibody response against zoonotic coronavirus SARS-CoV-2 responsible for pandemic COVID-19 disease. Two specific linear B-cell epitopes namely S1P4 and S2P6 have been recently identified in the SARS-CoV-2 spike protein expressed by the COVID-19 mRNA BNT162 vaccine of Pfizer-BioNTech and marketed under the brand name Comirnaty. The present study aimed at investigating the immunogenic potential of AuNPs functionalized with synthetic PADRE^S1P4 and PADRE^S2P6 peptides in a mouse model. The AuNPs were synthesized using an environmentally friendly process. In both synthetic PADRE^S1P4 and PADRE^S2P6 peptides, the SARS-CoV-2 spike antibody epitope is preceded by a polybasic sequence and the T-helper cell response activator PADRE. A thiol-terminated polyethylene glycol was used to decorate AuNP surface with the synthetic peptides. The AuNPs-peptide conjugates were inoculated without any adjuvant to adult BALB/c mice by intramuscular route in a prime-boost schedule. The AuNPs functionalized with the PADRE^S2P6 peptide but not the PADRE^S1P4 peptide were efficient to elicit antibody production of relevant specificity against the SARS-CoV-2 spike protein. The ability of PADRE^S2P6 peptide-reactive antibodies to recognize SARS-CoV-2 variants opens important perspectives for AuNP-peptide conjugates as potential serological tools to support the surveillance of wildlife-origin coronaviruses.