How to escape comma in csv file without using double quotes/" in C#

using (DataTable dt = new DataTable())
            {

                dt.Load(reader);
                Console.WriteLine(dt.Rows.Count);  //check its filled 
                StringBuilder sb = new StringBuilder();
                string sbb = "";
                sb.AppendLine(string.Join(",", dt.Columns.Cast<datacolumn>().Select(c => c.ColumnName)));
                sb.Remove(sb.Length - 1, 1);
                foreach (DataRow row in dt.Rows)
                {

                    for (int i = 0; i < dt.Columns.Count; i++)
                    {

                        if (row[i].ToString().Contains(","))
                        {

                            sb.Append(String.Format("\"{0}\",", row[i]));
                        }
                        else
                        {
                            sb.Append(row[i].ToString() + ",");
                        }

                    }



                    sb.AppendLine();

                }

                ArrayList ar = new ArrayList();


                File.WriteAllText(@"D:\ISR\1" + ".csv", sb.ToString());



            }