gistfile1.cs

 public static class StringExtensions
    {

        public static readonly string CHAR_UNICODE_HEX_FORMAT = "{0:x4}";
        public static readonly string CHAR_UNICODE_PREFIX = "&#{0};";
        
        public static string EncodeUnicodeChars(this string srcString)
        {
            if (srcString == null)
            {
                throw new ArgumentNullException("srcString");
            }
            
            return srcString.Aggregate(new StringBuilder(),
                                                              (sb, 
                                                                currrentChar) => 
                                                                                {
                                                                                    var charNumberValue = int.Parse(String.Format(CHAR_UNICODE_HEX_FORMAT, 
                                                                                                                                    (int)currrentChar),
                                                                                                                       NumberStyles.HexNumber);
                                                                                    
                                                                                    sb.AppendFormat(CHAR_UNICODE_PREFIX, charNumberValue);
                                                                                    return sb;
                                                                                },
                                                                sb => sb.ToString());


            
            
        }