nanopipettes

Nanopipettes are nanoscale versions of glass or quartz pipettes, with tip diameters ranging from a few nanometers to several hundred nanometers. They function as both fluidic carriers and electrodes, enabling precise control of tiny sample volumes and measurements of ionic currents at the nanoscale. Their small, conical tips give high spatial resolution and unique electrical properties ideal for probing chemical and biological processes in liquids.

Fabrication typically involves heating and pulling standard borosilicate glass capillaries in a micropipette puller, or using laser-based techniques for tip refinement. Tips can be further sharpened or shaped by chemical etching or focused ion beam milling. An internal electrode is inserted into the bore to form a working electrode, while an external reference electrode closes the circuit. The geometry of the tip and the surrounding meniscus governs access resistance and the sensitivity of current measurements.

Applications span several fields. In nanopore sensing, a pore is formed at or near the tip, and an applied voltage drives ion flow; translocating molecules produce transient current blockades that reveal information about size, charge, or conformation. Nanopipettes are also used as nanoelectrodes for localized measurements of ion concentration, pH, and electric fields, and as probes in scanning ion conductance microscopy (SICM) for non-contact topographic mapping of delicate samples.

Challenges include tip clogging, mechanical fragility, and electronic noise arising from access resistance and surface interactions. Reproducible fabrication, careful calibration, and appropriate surface chemistry are essential for reliable quantitative measurements. Nanopipettes continue to be a versatile tool for high-resolution sensing, single-molecule studies, and nanoscale electrochemical investigations.