Self-Assembled Nanoparticle Dimer Antennas for Plasmonic-Enhanced Single-Molecule Fluorescence Detection at Micromolar Concentrations

Plasmonic antennas offer extremely promising strategies to enhance single molecule fluorescence sensing and breach the limitations set by diffraction. However, the technical difficulty and limited availability of top-down nanofabrication techniques enabling nanometer gap sizes are limiting the impact of plasmonic antennas for biochemical and biophysical applications. Here we demonstrate the effectiveness of self-assembled nanoparticle gap antennas to enhance single molecule fluorescence detection at high concentrations. For a dimer of 80 nm gold nanoparticles with 6 nm gap, we isolate detection volumes down to 70 zL (equivalent to λ³/3600) and achieve 600-fold fluorescence enhancement, microsecond transit time, and operation of fluorescence correlation spectroscopy at concentrations exceeding 10 μM. We quantify the near-field detection volume and the fluorescence enhancement for different self-assembled nanoantenna designs using fluorescence correlation spectroscopy. The combination of the fabrication simplicity with the large fluorescence enhancement makes the self-assembled colloidal nanoparticle gap antennas optimal to extend a wide variety of single-molecule applications toward the biologically relevant micromolar concentration regime.