Touching a door knob before washing after waking up

Question

Should I be concerned about touching my door knob to go into another room to wash upon awakening? My guess is that it is aluminum which is generally said not to contract tumah but I am kind of curious about other materials that might be better, which ones to avoid and how they can be purified. I understand there is not a clear reason why we wash but I was taught that it is to remove tumah and not to touch food, clothes or orfices. Thanks