Nanobodies (Nbs) in virology and viral diseases: Applications in viral detection, neutralization, and therapy.

Nanobodies (Nbs), also known as variable domains of camelid heavy-chain-only antibodies (VHHs), have emerged as promising biomolecules in antiviral diagnostics and therapeutics because of their small molecular size, high stability, strong antigen-binding affinity, and ease of genetic engineering. Compared with conventional monoclonal antibodies (mAbs), Nbs exhibit superior tissue penetration, improved access to cryptic epitopes, cost-effective microbial production, and enhanced physicochemical stability under harsh environmental conditions. These properties make them attractive candidates for applications in viral detection, neutralization, intracellular targeting, imaging, and targeted drug delivery. Recent advances in Nb engineering have enabled the development of multivalent, bispecific, Fc-fused, and aerosolized Nb formats with improved pharmacokinetic and antiviral properties. Nbs have demonstrated promising activity against a broad range of viruses. Furthermore, Nbs have shown considerable utility in biosensors, ELISA systems, live-cell imaging, cryo-electron microscopy, and CRISPR-associated technologies. Despite these advantages, several challenges remain, including short serum half-life, potential immunogenicity, rapid renal clearance, and the need for large-scale clinical validation. This review summarizes the structural and functional characteristics of Nbs, discusses their antiviral mechanisms and engineering strategies, and highlights their expanding applications in viral diagnostics and therapeutics, along with current limitations and future translational perspectives.