gistfile1.cs

public const string CharUnicodeFormat = "&#{0};";
        
public static string EncodeUnicodeChars(this string text) {

  if (text == null) {
    throw new ArgumentNullException("text");
  }
         
  return text.Aggregate(
    new StringBuilder(),
    (sb, ch) => sb.AppendFormat(CharUnicodeFormat, (int)ch),
    sb => sb.ToString()
  );
}