Crust on toenail

My poor cat has blackish crust at the base of his nail, and it seems to be painful (as he let me know while I took this photo). I have an appointment with the vet in a few days, but was wondering if there are any home remedies that might make him feel better in the meantime. Some quick searching suggests that this might be a fungal infection but I couldn't figure out what sort of over-the-counter medicines work for the condition. If my best bet is to just wait for the vet visit, that's an OK answer too

Thanks!

Gosh, it could be caused by bacterial or fungal infection, or even something else.  Is he licking at it quite a bit?  Hard to say what to do about it not knowing the cause. However, I did see that an antimicrobial soak might be a good place to start, although not sure where you would find that. 

The nailbed isn't inflamed, is it?  And it's just that one claw, right?  When is your Vet appointment?