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 microg/mL with a detection limit of approximately 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.