Multiplex immunodetection of tumor markers with a suspension array built upon core-shell structured functional fluorescence-encoded microspheres

A new suspension array built upon laboratory-prepared functional fluorescence-encoded polystyrene beads (FFPBs) was developed for multiplex immunodetection of tumor markers. The FFPBs were synthesized by copolymerizing rhodamine 6G (R6G) and carboxyl function groups on the surface of the seed beads forming a core-shell structure. The fabrication process was facile and the encoding fluorescence intensity of the beads can be precisely controlled by adjusting the quantity of R6G. In present work, we demonstrated that the quantity variation of impregnated R6G had negligible effect on the coupling efficiency of biomolecules onto the surface of the FFPBs. The R6G encoding fluorescence remained good monodispersity upon capture probe coupling and immunocomplex formation. No fluorescence resonance energy transfer was observed between the R6G doped in the bead shell and fluorophore used for antibody labeling. Under the optimal conditions, the proposed suspension array allowed simultaneous detection of α-fetoprotein, carcinoembryonic antigen, and prostate specific antigen in the ranges of 0.07-500 ng mL⁻¹, 1-2000 ng mL⁻¹, and 0.5-500 ng mL⁻¹, respectively, with detection limits of 0.0626 ng mL⁻¹, 0.554 ng mL⁻¹, and 0.250 ng mL⁻¹. Test on clinical serum samples demonstrated that the results obtained with suspension array were in good agreement with those of the reference electrochemiluminescence immunoassay method. We conclude that the laboratory-made FFPBs are sufficient as the microcarrier for the construction of suspension array in clinical diagnosis.