FindElement(By.CssSelector("[dd:concept='TITLE']")) should work.
Ah, you're using ruby.
I did a bit of looking, you could try this:
find_element(:css, "[dd:concept='TITLE']")
Edit once again.
I would suggest escaping the : in the tag name dd:concept, like this:
find_element(:css, "[dd\:concept='TITLE']")