Advantage of Eu3+‐Doped Polystyrene Microspheres Compared with Colloidal Gold Used in Immunochromatographic Assays for the Detection of Melamine in Milk

Colloidal gold and Eu³⁺‐doped fluorescent microspheres were applied as labels to develop the immunochromatographic strips for detecting melamine in milk. Under the optimized condition, the visual detection limit of colloidal gold‐immunochromatographic test strip (ICTS) was 150 μg/L of melamine in phosphate‐buffered saline (PBS), although the visual detection limit of fluorescent nanoparticles (FN)‐ICTS was 75 μg/L in PBS. As thermal acceleration test, FN‐ICTS could be stored at 37 °C for at least 11 d before sample testing, but the color of the lines on colloidal gold‐ICTS faded away after 7‐d storage. The visual result of FN‐ICTS was more stable than that of colloidal gold‐ICTS, and the fluorescence intensity of the line on FN‐ICTS could be maintained up to 30 d at 22 °C after sample testing. Once the immunochromatographic strips were used to detect melamine in milk, no negative effect of milk components on the performance of FN‐ICTS was identified, whereas the performance of colloidal gold‐ICTS was significantly influenced by milk matrix.