A fast and sensitive immunoassay of avian influenza virus based on label-free quantum dot probe and lateral flow test strip.

A novel fluorescence immunoassay method for fast and ultrasensitive detection of avian influenza virus (AIV) was developed. The immunoassay method which integrated lateral flow test strip technique with fluorescence immunoassay used the label-free and high luminescent quantum dots (QDs) as signal output. By the sandwich immunoreaction performed on lateral flow test strip, the gold nanoparticle (NP) labels were captured in the test zone and further dissolved to release a large number of gold ions as a signal transduction bridge that was detected by the QDs-based fluorescence quenching method. Under the optimal conditions, the relative fluorescence intensity of QDs was linear over the range of 0.27-12 ng mL(-1) AIV, and the limit of detection was estimated to be 0.09 ng mL(-1) which was 100-fold greater than enzyme-linked immunosorbent assay (ELISA). The sensitive and specific response was also coupled with high reproducibility in the proposed method. A series of six parallel measurements produced reproducible fluorescent signals with a relative standard deviation of 4.7%. The proposed method can be used to directly detect clinical sample without any pretreatment, and showed high efficiency (90.0%), sensitivity (100.0%) and specificity (88.2%) compared with virus isolation (gold method). The new method shows great promise for rapid, sensitive, and quantitative detection of AIV in-field or point-of-care diagnosis.