A hypodermic needle PO2 electrode.

Several glass-covered gold wires (5-10 micrometer diam) connected to an insulated lead wire are embedded with epoxy inside a stainless steel needle (e.g., 25 gauge). The epoxy, glass, and gold wire are carefully ground off down to the bevel of the needle, and the gold wires recessed electrolytically using NaCN. Oxygen tension (PO2) is measured polarographically, usually using a separate Ag-Agcl reference electrode. However, the stainless steel needle, connected to the shield of the coaxial lead, can also be used as the reference. The PO2 electrode shows little or no stir sensitivity and has a response time (to 100%) of 1-2 s.