Transmit command and receive data from microcontroller via RS232

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.IO.Ports;
using System.Threading;
using System.IO;

namespace GTPT_688
{
    public partial class Form1 : Form
    {
        //byte ack = 0;
        //byte[] buff;
        string valueOfTemperature;
        public Form1()
        {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            //configuring the serial port
            serialPort1.PortName = "COM5";
            serialPort1.BaudRate = 19200;
            serialPort1.DataBits = 8;
            serialPort1.Parity = Parity.None;
            serialPort1.StopBits = StopBits.One;
            serialPort1.DtrEnable = true;
            serialPort1.RtsEnable = true;
            //valueOfTemperature = 0;
            //buff = new byte[1];
            if (!serialPort1.IsOpen)
            {
                try
                {
                    serialPort1.Open();
                }
                catch (System.Exception ex)
                {
                    MessageBox.Show(ex.ToString());
                }
            }
            serialPort1.DataReceived += new SerialDataReceivedEventHandler(serialPort1_DataReceived);
        }
        private void Form1_FormClosed(object sender, FormClosedEventArgs e)
        {
            if (serialPort1.IsOpen)
            {
                serialPort1.Close();
            }
        }
       private void Send_Click(object sender, EventArgs e)
       {
           if (ck1.Checked == true)
           {
               byte[] mBuffer = new byte[1];
               mBuffer[0] = 0x6F; //ASCII for o;.
               serialPort1.Write(mBuffer, 0, mBuffer.Length);
           }
           if (ck1.Checked==false)
           {
               byte[] mBuffer = new byte[1];
               mBuffer[0] = 0x66; //ASCII for f;.
               serialPort1.Write(mBuffer, 0, mBuffer.Length);
           }
                if (ck2.Checked==true)
                {
                    byte[] mBuffer = new byte[1];
                    mBuffer[0] = 0x74; //ASCII for t;.
                    serialPort1.Write(mBuffer, 0, mBuffer.Length);
                }
        }
        private void serialPort1_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
               valueOfTemperature += serialPort1.ReadExisting();
               this.Invoke(new EventHandler(DisplayText));
        }
        private void DisplayText(object sender, EventArgs e)
        {
            //if (sender == serialPort1)
            //byte[] buff = new byte[serialPort1.BytesToRead];
            //serialPort1.Read(buff, 0, buff.Length);
            //string str = Encoding.ASCII.GetString(buff);
                lb1.Text = valueOfTemperature;
        }
        private void bn1_Click(object sender, EventArgs e)
        {

        }
    }
}