There is no such data type as "binary", so the question is simply ambiguous. As we don't know what is your purpose, you cannot get on definitive answer.
However, you can represent any string in certain encoding used for binary representation of Unicode. The encoding has to be one of the UTFs, as other encodings will cause the loss of data, as the cannot represent all Unicode code points.
For example, for UTF-8 (most popular encoding used to represent Unicode text in text files and on Internet), it would look like this:
string myString =
System.Text.Encoding encoding = System.Text.Encoding.UTF8;
byte[] data = encoding.GetBytes();
string text = new string(encoding.GetChars(data));
—SA