Maybe it´s just bad google fu, but I can´t seem to find what the Dexcom sensor wire and/or the coating consists of.
All i find is that the sensor wire is made of silver and platinum metal with polymer membranes. No more spesifics on the membranes.
Reason I ask is that I just found out that I´m allergic to cobalt, so if cobalt is used either by itself or in an alloy, that could explain my trouble with Dexcom lately.
The wire as you found is silver and platinum. It is possible that there is cobalt in the wire. I would think not, because cobalt is rather unfriendly to living beings. The polymer membrane near as I can determine is Gluocose oxidase which should not contain any cobalt.