systax error

Question

incorect syntax near '1'.                        there is only 1 in date time picker

 SqlCommand cmdd = new SqlCommand("INSERT INTO investor_detail (investor_id,investor_cnic,investor_amount,date,pay_amount,remaining_amount ) VALUES ('" + a + "','" + b + "','" + investoramount.Text + "','" + dateTimePicker1.Value + "','" + payamount.Text + "','" + remainnigamount.Text + "'", my);
                        cmdd.ExecuteNonQuery();