In this sentence,
My research for Point of Origin was some of the most intensive and dangerous I've done to date, and the story I tell here remains the most painful. (Seen at the introduction part of novel, "Point of Origin", by an American writer)
Can we say "to day" instead of "to date" in the above sentence? Because "today" comes from "to day", though I'm not sure about whether we can still use "to day".