Dowben Rose Microelectrode
Dowben and Rose developed a special electrode to study chemical changes and reactions in very fine structures. We used that design to study what signals issued at the cut end of axons in the optic nerve of a live frog.
A standard glass microelectrode is drawn with tip diameter of about ten micrometers. It is filled over a hot plate by a thin slug of low melting point alloy (Cerraloy 136) thrust by a stiff copper wire that imbeds in the alloy as the tip fills. The small ball of alloy that forms at the tip is wiped off between thumb and forefingers. The exposed metal at the tip is then electroplated with a thin film of gold (from Dalic gold solution) then capped with Platinum black (from chloroplatinic acid solution). This capping does not exceed the outer diameter of the tip, and forms a shallow micro-dome on the tip.