Characterization of the fluorescence 'dead zone'. The 'on/off' fluorescence behavior observed during liposome multipassing, Figure and Figure , is hypothesized to result from scattering of the excitation light (488 nm) at the tip of the subwavelength nanopipette orifice (110150 nm radius). This fluorescence 'dead zone' just outside of the nanopipette orifice was investigated by multipassing a ~100 nm radius fluorescent PS nanoparticle using longer external delay times (10 ms), enabling the particle to pass entirely through the 'dead zone' and into the external electrolyte solution where it begins to emit fluorescence again due to a portion of the excitation light traveling through the transparent glass walls of the nanopipette (Figure , Figure ). Figure shows a series of images during the multipassing of the ~100 nm radius fluorescent PS nanoparticle passing through the 'dead zone'. Based on the images, the 'dead zone' extends ~1.5 m from the tip of the nanopipette into the external solution. The observed width of the 'dead zone' was not influenced by changing the velocity of the translocating PS nanoparticle suggesting that this region originates from the geometric constraints of the subwavelength nanopipette orifice size (Figure ). Sizing liposomes with multipass resistive-pulse sensing. The radius of multipassed spherical particles can be calculated from the maximum blockage current of the resistive pulse, %Δi, as %Δi is proportional to the volume of the particle. Eq. 1 describes the relationship between the percent blockage current and the particle radius, r, where the proportionality constant, k, is related to the orifice size of the nanopipette. The value of k was determined by adding PS nanoparticles of known nominal radii to the liposome solution. Both the liposomes and PS nanoparticles were detected by resistive-pulse sensing and the average %Δi was determined for the PS particles (Figure ). %∆𝑖 = 𝑘𝑟 (1)