Figure 2: (A and B) Cy3/Cy5 smFRET traces measured at 100 mM MgCl2 for duplex on (A) quartz and (B) the grating surface; (C-F) smFRET traces of duplex localized in the nanocavity measured at (C) 10 mM, (D) 100 mM, (E) 300 mM, and (F) 1 M MgCl2. The data for quartz substrate was taken with TIRFM, and those for gratings and nanocavities were taken with epi-fluorescence microscope.