Technique for precision beveling of relatively large micropipettes

A technique is described for embedding various sizes of diamond dust in a film of Varathane laid upon an optically flat glass surface. This forms a precise and very durable abrasive surface. When such abrasive surfaces are used with previously described equipment, micropipettes may be beveled rapidly and reliably to tip diameters extending from 0.5 micron to indefinitely large sizes. Beveled tips formed in this manner are extremely sharp, as shown by high resolution SEM photographs. Plugging of the micropipette tip during beveling is prevented by applying pressure to the contained electrolyte. This procedure allows the micropipette's electrical resistance to be monitored accurately and continuously, so that beveling may be stopped at the electrical resistance associated with any predetermined tip diameter. The beveling of such relatively large micropipettes appears to have a variety of applications in neurophysiology, plus additional applications in kidney and capillary micropuncture work.