Highly sensitive grating coupler-based surface plasmon-coupled emission (SPCE) biosensor for immunoassay

We have evaluated the performance of a novel high-content gold grating coupler-based surface plasmon-coupled emission (SPCE) biosensor system. The polyelectrolyte (PEL) layer on the system's biosensor chip surface was formed on the gold surface using a layer-by-layer (LbL) deposition technique to spatially separate fluorophores from the gold surface and as a linker layer for protein immobilization. The characteristics of the PEL spacer layers were determined by surface plasmon resonance (SPR) analysis and by ellipsometry. The SPCE response decreased as the spacer layer thickness increased above a dominant quenching range (10 nm). Two PEL layers of poly(diallyldimethylammonium chloride) and poly(acrylic acid) were found to be an effective spacer that minimized the quenching effect while maximizing SPCE responses for both direct and sandwich immunoassay formats. A mouse IgG sandwich immunoassay using this optimized spacer layer configuration showed a dose-dependent response with a 1 pg ml−1 limit of detection by the 3σ rule. A nine log dynamic range of human IgG concentrations in unfractionated human serum could be analyzed using this approach. These results show the potential of the grating coupler-based SPCE biosensor as a sensitive platform for high-content analysis.