Conjugated polymer as a signal amplifier for novel silica nanoparticle-based fluoroimmunoassay

Immunoassays are conventional methods for protein detection, which rely on specific antibody–antigen recognition. Very few strategies have been developed for signal amplification of immunoassays. In this work, we report a conjugated polymer amplified silica nanoparticle (NP)-based immunoassay for IgG detection. After immobilization of the prime antibody on the NP surface, the NPs are used to capture antigen and Cy3 labeled secondary antibody in a sandwich assay format. The presence of target antigen in solution brings the fluorescent Cy3 molecules to the NP surface. Addition of a cationic conjugated polymer further amplifies the fluorescence signal of the dye, which improves the assay sensitivity and selectivity. Within the tested concentration range, a linear response for IgG detection is observed from 0 to 1 μg/mL with a detection limit of ∼1.1 ng/mL. Due to the pink color of Cy3 molecules, the assay also allows naked eye detection of IgG with a detection limit of 50 ng/mL. The polymer amplified NP assay represents a simple strategy for antigen detection with high sensitivity and selectivity.