How can I prefix the converted hex value with hex escape value '\x' in C#

       private void button1_Click(object sender, EventArgs e)
       {
           Open();
           string str = "نص";
           string str1 = ToHexString(str);
           textBox1.Text = str1;
           StringBuilder receipt = new StringBuilder();
           receipt.Append("\x1B\x40");         // Initialize Printer
           receipt.Append("\x1B\x74\x28");     // Select Arabic code page (Page 40,1256)
           receipt.Append(str1);               // The Arabic text to be printed
           receipt.Append("\x0A");             // Print and line feed
           receipt.Append("\x1D\x56\x42\x00"); // Select cut mode and cut paper
           string szString = receipt.ToString();
           PrintText(Printer, szString);

       }


public string ToHexString(string str)
       {
           var sb = new StringBuilder();
           var encoding = Encoding.GetEncoding(1256);
           var bytes = encoding.GetBytes(str);
           foreach (var t in bytes)
           {
               sb.Append(t.ToString("X2"));
           }
           return sb.ToString();
       }