Metallic nanostructures supporting collective localized surface plasmons (cLSPs) are investigated for the amplification of signal in fluorescence biosensors. cLSPs modes are supported by diffractive arrays of metallic nanoparticles that are embedded in a refractive index-symmetrical environment. They exhibit lower damping and thus their excitation is associated with higher field intensity enhancement and narrower resonance than that for regular localized surface plasmons. Through finite difference time domain (FDTD) simulations, we designed a novel cLSP structure that exhibit two resonances overlapping with absorption and emission wavelengths of assumed fluorophore (similar to Cy5 or Alexa Fluor 647). The simulations of surface plasmon-enhanced fluorescence (PEF) took into account the cLSP-driven excitation, directional emission, and mediated quantum yield in realistic sandwich immunoassays that utilize fluorophore-labeled detection antibodies. Achieved results indicate that cLSP-based structures holds potential for extraordinarily high fluorescence intensity enhancement that exceeds a value of 10(3).