C# String.Format with Curly Bracket in string

Possible Duplicate:
Escape curly brace '{' in String.Format

c# has a String.Format method that allows you to format a string but inserting params with the tokens {0} {1}

I am trying to create a simple json string which requires curly brackets to be in the string, and so it is breaking the formatter

String.Format("{ foo:'{0}', bar:'{1}' }", foo, bar);

Adding an escape before the braces did not help

Throws a exception saying my string is incorrectly formatted, anyone know how to get around this?