[Show abstract][Hide abstract] ABSTRACT: A nanoparticle-based immunoassay was developed for the rapid and sensitive detection of avian influenza virus (AIV). In this method, AIV-specific pentabody (pVHH3B) was conjugated to magnetic nanoparticles (MNPs) and used to capture AIV. Gold nanoparticles (GNPs), labelled with the anti-AIV mouse monoclonal antibody 3C8, were used as a detector. In the presence of target samples, the pentabody pVHH3B enriched AIV on the MNPs. Thereafter, mAb 3C8-labelled GNPs (GNPs-mAb3C8) bound to MNPs via AIV and were separated using a magnetic field. GNPs in the complex catalyzed the oxidation of hydroquinone to quinone, and the OD value of quinone was measured. The developed assay displayed substantial signal change after incubation in an AIV sample in a concentration-dependent manner. The detection limit was 10 ng/ml, which is 10 times more sensitive than conventional double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). In conclusion, by combining MNPs and a novel pentabody pVHH3B, this study provided a sensitive influenza viral detection assay that has the potential to become a rapid, sensitive and inexpensive diagnostic tool for infectious diseases.