Liquid glass electrodes for nanofluidics

Nanofluidic devices exploit molecular-level forces and phenomena to increase their density, speed and accuracy1. However, fabrication is challenging because dissimilar materials need to be integrated in three dimensions with nanoscale precision. Here we report a three-dimensional nanoscale liquid glass electrode (NLGE) made from monolithic substrates without conductive materials by femtosecond laser nanomachining. The electrode consists of a nanochannel terminating at a nanoscale glass tip that becomes a conductor in the presence of high electric fields through dielectric breakdown, and returns to an insulator when this field is removed. This reversibility relies on control of nanoampere breakdown currents and extremely fast heat dissipation at nanoscale volumes. We use the NLGE to fabricate a nano-injector that includes an electrokinetic pump, 4 µm across with 0.6 µm channels, and capable of well-controlled flow rates below 1 fL/s. The electrode can be easily integrated into other nanodevices and fluidic systems, including actuators and sensors.