A silica nanoparticle based 2-color immunochromatographic assay for simultaneous determination of clenbuterol and ractopamine

An immunochromatographic assay (ICA) is presented that can be applied to simultaneous detection of clenbuterol (CLE) and ractopamine (RAC). It is making use of two red and blue silica nanoparticles (SiNPs) that act as labels for encoding the antibodies. This design permits multiplexed analysis in a single test line and does not require an external source for photoexcitation. Anti-CLE was labeled with red SiNPs, and anti-RAC with blue SiNPs. The capture antigens CLE-BSA and RAC-BSA were placed onto the conjugate pad and the test line of the test strip, respectively. Under bare eye examination, no cross-colored lines or nonspecific bioconjugate adsorption were observed, and the visible limit of detections for CLE (red) and RAC (blue) are 3 and 2 ng‧mL −1 , respectively. This design allows for multiplexed detection with reduced device dimensions and costs, and with easy integration and manufacturing. Conceivably, the method may be extended to simultaneous determination of numerous other analytes. The principle of qualitative detection strategy of multiplex immunochromatographic assay for clenbuterol (CLE) and ractopamine (RAC) is schematically illustrated. Depending on the type and ratio of organic dyes, the color of colored silica nanoparticle can be tuned from red to purple and even to black (lower right corner).