Magnetic bead-based mimic enzyme-chromogenic substrate and silica nanoparticles signal amplification system for avian influenza A (H7N9) optical immunoassay

This work reports on a simple, feasible and optical color-enhanced colorimetric immunoassay with hemin (a horseradish peroxidase mimic enzyme) catalyzed color reaction and multifunctional colored silica nanoparticles for qualitative and quantitative determination of avian influenza A (H7N9) virus (H7N9 AIV) at an ultralow concentration by using the magnetic nanobeads (MBs)-mimic enzyme-multifunctional silica nanoparticles color-enhanced chromogenic substrate system. In this work, MBs were fabricated by co-immobilizing target recognition molecules (mAb–MB), which were used as both separation and enrichment carriers. The multifunctional colored silica nanoparticles were synthesized by doping Cy2 (red organic dye) into silica nanoparticles using an inverse microemulsion method, and then made a covalent modification of pAb and glucose oxidase (GOx). In the presence of H7N9 AIV, GOx catalyzed glucose to gluconic acid and hydrogen peroxide (H2O2). The latter can oxidize 4-aminoantipyrine (4-AAP) to red products and the reaction is catalyzed by hemin. The chromogenic compound and the red-silica nanoparticles (Red-SiNPs) together cause the color of the solution to change from colorless to red. Through this color-enhanced immunoassay, we can detect H7N9 AIV with the naked eye and UV detector. And the immunosensor provides a simple and reliable platform with high sensitivity and selectivity which shows great potential in early diagnosis of diseases and in public health security.