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

The stabilities of core-shell purple silica nanoparticles (core-shell purple SiNPs) and colloidal gold were compared in solutions with different concentration of salt (left) and different pH (right), respectively. An immunochromatographic strip based on core-shell purple SiNPs for detection of clunbuterol (CLE) has been developed. It was based on competitive reaction between the CLE-BSA (test line) and the target CLE to combine with anti-CLE antibody-modified core-shell purple SiNPs conjugates. As is shown in the figure, when there is no CLE in the sample, purple band would appear both at test and control line. Otherwise, no color or reduced purple color intensity at the control line compared with the negative sample. [Display omitted] •The colored silica nanoparticles (colored SiNPs) were first used as label to develop an immunochromatographic strip.•Core-shell purple silica nanoparticles (core-shell purple SiNPs) based ICA was successfully developed for detection of clenbuterol (CLE).•The synthesis and functionalization procedures of core-shell purple SiNPs were presented in detail.•Two real samples with simple pretreatment spiked CLE standard have been tested in this work. 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.