iOS Split NSString into array of characters?

Is there a way to split a string into an array of individual characters? I've tried this but it doesn't seem to work:

NSString *foo = @"The quick brown fox";
NSArray *chars = [foo componentsSeparatedByString""];

But then the length of chars is 1, and chars[0] contains the entire string rather than just "T".

I must be missing something obvious...