Recording Pipettes

Pulling Electrode Glass

I usually pull the electrode glass to a tip diameter of about 5 µm. This is a general-purpose size which yields resistances of around 3 to 5 MOhms after fire-polishing.

Sylgard

Sylgard (polydimethylsiloxane, or PDMS) is an insulating agent that reduces pipette capacitance. Coating the tip of the recording pipette with Sylgard lowers noise during single channel recording and improves resolution of fast events. However, Sylgard is not necessary for many exeriments in the whole cell configuration, especially when precise kinetic measurements are not necessary. A nice tool to apply Sylgard to the pipette tip can be made from pipette glass simply by heating the end until it fuses together. Coat the shank of the recording pipette, coming as close to the tip as possible. The Sylgard can be hardened by drawing it through a coiled heating element. Be careful to heat the tip first to prevent flowing Sylgard from occluding the opening. Twist the pipette and draw the Sylgard-coated section through the heating coil several times until it appears hard. Sometimes the Sylgard will still be quite sticky. You can touch the end of a fine forceps to the Sylgard to test whether further heating is necessary. If you have problems with the Sylgard flowing into the pipette tip, back off a little from the tip when you first coat the shank.

 

Fire-Polishing

Formation of gigaohm seals is improved by fire-polishing the tip of the recording pipette. However, fire-polishing is not necessary for gigaseal formation. Many labs have abandoned this practice, although it is probably wise to have a microforge on hand in case of problems.

Fire polishing of the micropipette tip.