Pulled glass nanopipettes were fabricated using a P-2000 laser puller (Sutter Instruments). Quartz capillaries (1.0 mm outer diameter, 0.7 mm inner diameter, Sutter Instruments) were pulled using a single line program with the following parameters: heat: 560 filament: 3, velocity: 30, delay: 145, pull: 175. The orifice of the nanopipettes were sized by measuring the pressure to extrude bubbles from the pipette tip in 200-proof ethanol. Pipettes were backfilled using a Microfil syringe tip (MF28G, World Precision Instruments) with 0.1 M NaCl and 10 mM PB (pH 7).