Fabrication of well defined micropipette tips by hydrofluoric acid etching.

Glass tubes were drawn on a two stage pipette puller such that tips with 0.5-2.0 micron inner diameters were obtained as confirmed by scanning electron imaging. The pipettes were attached to an air reservoir with a pressure set at 0.5 bar to prevent fluid from entering the tip. They were lowered into 2% hydrofluoric acid by means of a micromanipulator. When air bubbles began to escape from the tips, they were withdrawn and immersed into 0.5 molar phosphate buffer, pH 7.4, and then rinsed with tap water and ethanol. Etching during 100 s (mean) yielded inner tip diameters of 5 micron (+/- 5% S.D.). The tips were beveled at the same angle at which they had been dipped into the etching fluid. No continuation of the etching process was noticed even after several days.