Immunochromatographic assay using brightly colored silica nanoparticles as visible label for point-of-care detection of clenbuterol

A novel immunochromatographic assay (ICA) using colored silica nanoparticles (colored SiNPs) as optical directly-detected label was developed for point-of-care detection of clenbuterol (CLE). To our knowledge, this is the first report that using colored SiNPs as nanolabel to develop an ICA. CLE was selected as the model analyte for competitive ICA. The coloration of monodispersed silica nanoparticles (SiNPs) was preceded in water with the presence of aminosilanes and C.I Reactive Violet 5. The purple SiNPs were introduced into a pre-hydrolyzed Stöber system to regrow a silica shell, forming core-shell purple SiNPs. The silica shell prevented dye on SiNPs from leaking. Under appropriate conditions, the core-shell purple SiNPs based ICA was developed to screen for CLE detection by naked eyes at cut-off values of 3 ng/mL, 6 ng/mL and 5 ng/mL in phosphate buffered saline, urine and pork, respectively. The core-shell purple SiNPs based immunoassay system has no cross activity with other nonspecific structural analogues. The results showed that colored SiNPs are promising to be alternative visible labels for the ICA strip.