We introduce an innovative design of planar plasmonic nanogap antenna arrays and demonstrate its potential to study thespatiotemporal organization of mimetic biological membranes at the nanoscale. We exploit our novel nanogap antennaplatform with different nanogap sizes (10-45 nm) combined with fluorescence correlation spectroscopy to reveal theexistence of nanoscopic domains in mimetic biological membranes. Our approach takes advantage of the highly enhancedand confined excitation light provided by the antennas together with their extreme planarity to investigate membraneregions as small as 10 nm in size with microsecond temporal resolution. We first demonstrate the ultra-high confinementof photonic antennas on biological membranes. Moreover, we show that cholesterol slows down the diffusion of individualfluorescent molecules embedded in the lipid bilayer, consistent with the formation of nanoscopic domains enriched bycholesterol. Incorporation of hyaluronic acid (HA) to the ternary lipid mixture further slows down molecular diffusion,suggesting a synergistic effect of cholesterol and HA on the dynamic partitioning of mimetic biological membranes.
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