Subject: What is special about the make-up of US currency, and the Chemistry in it?

I am doing a paper on counterfeit money and what chemistry has to do with 
it.  What does Chemistry have to do with real and counterfeit money.  and 
What is special about the make-up of US currency that allows "special 
iodine inkpens" to tell wether a bill is real of a counterfeit?  Why does 
the mark made by the pen turn black on fake bills, but remains yellow on 
real bills?  What is so special about the make-up of the paper used in US 
currency

Re: What is special about the make-up of US currency, and the Chemistry in it?