[Stu]

Before


After


I made a 'swipe' tool out of some thin bendy plastic. It took me a while to hunt about for something that had enough strength to apply some uniform pressure but was bendy enough to make sure it was delicate. I could also cut this to the exact right size for the sensor. I bent it double to make sure there was a nice radius over the end.
The wipes are www.whatman.com and the cleaning fluid is pure isopropanol alcohol. I was VERY careful to just dampen the wipe with cleaning fluid to avoid dirty fluid bleeding up the back of the sensor.