Sharpened Tungsten Needles

MATERIALS

Sodium nitrite or 10 n KOH (see Step 1)

Alligator clip

Beaker, small

Metal-handle needle and probe holder (Ted Pella)

Power supply (12 V)

Test tube mixer (e.g., Thermolyne Speci-Mix) (optional; see Step 3)

Tungsten wire, 0.010-in. diameter (A.D. Mackay, Inc. or Goodfellow)

1. Take a 12 V microscope power supply with continuous voltage regulation and remove insulation from one wire to make an electrode. Submerge this electrode in a small beaker containing H₂O saturated with sodium nitrite or 10 n KOH.
2. To the other lead, attach an alligator clip, so as to connect the lead to the metal part of the tungsten needle holder. Hold the needle and submerge the end of the wire into the solution.
3. Depending on the depth of submersion, make long sharp needles for puncturing (more submersion) or short blunter needles for dissection.
- Needles can be rapidly sharpened this way (∼1 min usually) if the need arises to resharpen while working. Another way to make the points is to attach the needle to a rocker assembly, e.g., a test-tube mixer, and arrange it so the needle dips in and out of the solution as the mixer rocks. This will make it easy to get tapered points.