Au/Fe(3)O(4) core–shell nanoparticles are an efficient immunochromatography test strip performance enhancer—a comparative study with Au and Fe(3)O(4) nanoparticles

Immunochromatography test strips that use metal particles constructed from Au, Fe(3)O(4), and Au/Fe(3)O(4) nanoparticles were developed for the rapid detection of avian influenza virus subtype H7 (AIV H7). The principle of this immunochromatography test strip was based on a sandwich immunoreaction in which AIV H7 antigens bind specifically to their corresponding antibodies on a nitrocellulose membrane. An antibody–metal (Au, Fe(3)O(4) or Au/Fe(3)O(4)) nanoparticle conjugate was used as a label and coated onto a glass fiber membrane, which was used as a conjugate pad. To create a test and a control zone, an anti-H7 polyclonal antibody and an anti-IgG antibody were immobilized onto the nitrocellulose membrane, respectively. Positive samples displayed brown/red lines in the test and control zones of the nitrocellulose membrane, whereas negative samples resulted in a brown/red line only in the control zone. The limit of detection (LOD) of the Au/Fe(3)O(4) nanoparticle-based immunochromatography test strips was found to be 10(3.5) EID(50) (EID(50): 50% Egg Infective Dose), which could be visually detected by the naked eye within 15 min. In addition, 200 clinical samples were tested using the Au/Fe(3)O(4) nanoparticle-based immunochromatography test strip to estimate its performance, and seven were positive for AIV H7. In summary, the Au/Fe(3)O(4) nanoparticle-based immunochromatography test strip offers a simple and cost-effective tool for the rapid detection of AIV H7.