Nikkormat 35mm SLR, 50mm f/1.4 Nikkor with lens reversing ring; scan of 35mm transparency

The outer metal tube is platinum, and has an outside diameter of 2.0 millimeters.
The dot on the face is the end of a gold wire, 60 microns
(a little more than two-thousandths of an inch) in diameter,
about the thickness of a piece of paper (or a human hair).

This coaxial ultramicroelectrode (UME) was something I designed and made during my
doctorate work in graduate school. The gold wire and platinum tube were electrically
connected to a BNC connector (at the opposite end shown in the photograph).
The gold wire was insulated with a teflon sleeve, and passed through the tube.
The space between the wire and the outer tube was filled with crushed,
low-melting point glass, and the glass melted with a torch. (Glass was used
because it is more chemically inert than epoxy resin, and also doesn't leach
out organic contaminants.) The end of the assembly was ground flush
and then polished to a mirror finish.

The electrode was used for high speed spectroelectrochemistry: a light beam
(from a laser or optically filtered xenon arc lamp) was focused on the gold "dot,"
and its reflected intensity monitored to study the rate of
chemical reactions in solution, initiated at the surface of the dot.
The coaxial geometry was needed to reduce the inductance,
one of the factors that determined the risetime.

The tube is beat-up because this was the second, successful attempt to make the electrode assembly.
Not about to throw away a platinum tube, so had to partially crush it to remove the glass for the second try.
I also built a "brother" to this UME assembly, except with 25 micron diameter
(about 1/1000 of an inch) platinum wire in the center.
That electrode helped to break the previous world "speed" record for establishing
a stable electrochemical potential (and by well over an order of magnitude).
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