Homogeneous, Competitive Fluorescence Quenching Immunoassay Based on Gold Nanoparticle/Polyelectrolyte Coated Latex Particles

This study reports a homogeneous and competitive fluorescence quenching immunoassay based on gold nanoparticle/polyelectrolyte (AuNP/PE) coated latex particles prepared by the layer-by-layer (LbL) technique. First, the resonant energy transfer from a layer of fluorescent PEs to AuNP in LbL assembled films on planar substrates was investigated. The quenching efficiency (QE) for the planar films depended on the cube of the distance between the two layers. A QE of 50% was achieved at a distance of ca. 15 nm, indicating that the AuNP/PE system is suitable for detecting binding/release events for antibodies. A homogeneous, competitive binding immunoassay for biotin was designed based on AuNP/PE-coated polystyrene particles of 488 nm diameter as quenching agents for a fluorescein isothiocyanate labeled anti-biotin immunoglobulin (FITC-anti-biotin IgG). Biotin molecules were localized on the AuNP/PE-coated latexes by depositing a layer of biotinylated poly(allylamine hydrochloride) (B-PAH), and FITC-anti-biotin IgGs were subsequently bound to the particles through interaction with the biotin on B-PAH. Transmission electron microscopy and quartz crystal microgravimetry confirmed the multilayer formation on latex particles and planar gold surfaces, respectively. The biotin-functionalized AuNP/PE-coated latexes terminated by FITC-anti-biotin IgG exhibited a dynamic sensing range of 1−50 nmol. These results indicate that AuNP/PE-coated latexes can be readily used as dynamic range tunable sensors.