A Silver-glass Micro-electrode for Use in a Micromanipulator

In an investigation of the neuro-motor mechanism of small blood vessels, 1 the author needed to make micro-electrodes for the stimulation of small nerve fibers. The non-polarizable type (micro-salt-bridge), described by Ettisch and Péterfi, 2 Taylor, 3 Gelfan, 4 and Field, 5 was not necessary. Various polarizable types described in the literature were found to be inadequate. The platinum-quartz micro-electrode, devised by Taylor 3 and used by Pratt and Reid 6 and by Steiman 7 for the study of single muscle fibers, proved to be expensive, required an oxygen flame to draw, and broke easily. The micro-electrode described by Sen 8 may be produced in quantity by the deposition of metallic platinum, gold, or silver on the surface of quartz or glass micro-needles, using Brashear's method for silvering glass or the method of sputtering with a high voltage discharge in a vacuum. Electrodes of this type had to be insulated individually by the application of shellac with a small brush. It was found that the insulation did not resist a strong faradic current.

A 3-inch length of silver suture wire (No. 28 or No. 30) was inserted in a closely-fitting, soft glass capillary and drawn in a minute gas flame to produce an insulated silver-glass micro-electrode. The type of micro-burner described by Chambers and Kopac 9 was used. When a satisfactory tip was obtained, the end of the silver wire was fused to a piece of copper wire. The copper wire and the initial portion of the shank of the electrode were then sealed in a 5-inch length of glass tubing (6 mm in diameter), by means of a beeswax-resin cement. This tube constituted the electrode holder and was inserted in an Emerson micromanipulator in place of the holder supplied with the instrument.