You should disassemble it a bit and dry the insides. I.e. get the necessary screwdriver and remove the whole back, not just the cover. It might have water in there.
I once dropped a nokia 808 in the tap, and I did this. It had water inside, which I dried. Also used compressed air afterwards. After a few hours of letting it dry, it was 100% fine.
Also, how do you nano-coat a cellphone???