Homebutton doesnt work after water contact

Hey Guys. First of all, it's possible, that my English is not very perfect. I'm sorry for any mistakes.

I have an iPhone 3G here, which has some problems with its homebutton.

Quite a nice story, it fell in a cup with artificial blood which was used to take a video for school.

The only thing that doesnt work now is the Homebutton.

I opened the iPhone to look where the blood (its a mixture of water and red colour) was.

Which part should I order?

Thank You very much and nice greetings from Germany!

Joe