A novel sensitive staphylococcal enterotoxin C1 fluoroimmunoassay based on functionalized fluorescent core-shell nanoparticle labels

A highly sensitive fluoroimmunoassay for the determination of staphylococcal enterotoxin C1 (SEC1) is proposed. It is based on the functionalized fluorescent core-shell nanoparticles as the labels coated with anti-SEC1 monoclonal antibodies in “sandwich” fluoroimmunoassay. With the simple, inverse microemulsion polymerisation method, the functionalized fluorescent core-shell nanoparticles were prepared easily. The preparation process produces a silica shell on the surface of the Ru(bpy)3Cl2 (Rubpy) dye with one step cohydrolysis of tetraethylorthosilicate (TEOS), and the coupling agent (3-aminopropy1)triethoxysilane (APS) provided the amine groups that can be used for biological conjugation. The nanoparticles were then labeled with the anti-SEC1 monoclonal antibodies and the antibody-labeled nanoparticles were successfully used for the determination of SEC1. The calibration graph for SEC1 was linear over the range 1.0–75.0 ng ml−1 with a detection limit of 0.3 ng ml−1. The regression equation of the working curve was IF = 24.583 + 0.6426[SEC1] (ng ml−1) (r = 0.9991). The relative standard deviation (RSD) for five parallel measurements of 25.0 ng ml−1 SEC1 was 2.5%. Furthermore, the application of fluorescence microscopy imaging in the study of the antibody labeling and sandwich fluoroimmunoassay with the functionalized fluorescent core-shell silica nanoparticles was also explored. The results demonstrate that the method offers potential advantages of easily labeling to the antibody, sensitivity, simplicity and reproducibility for the determination of SEC1 and is applicable to the determination of SEC1 in real samples and enables fluorescence microscopy imaging for the determination of SEC1.