Here's a Israeli Chabad Daf Yomi Shaila by Chavrusa told me:
In Israel, if you borrow Dollars, then its not considered "money" but "Peiros". This is a problem, because if when you borrow, say 1,000 dollars at a rate of 3.7 shekel to the dollar, and then pay him back when its 3.8 shekel to the dollar, you'll in effect be paying him back 100 shekel extra. That being so, the easy way to borrow without a problem of Ribbis is if you have a dollar on you that you could theoretically give as payment (even one dollar works). If you have that dollar, that loan is "based" on that dollar and the rate therefore gets "frozen".
The question is, though, if someone borrows dollars in Israel, and the only dollar he has is one that he received from the Rebbe Zta"l can we consider that enough to free the loan from Ribbis? Is the dollar considered by its face value or by the market value which would be much more than a dollar?