How to create a SerialPort.ReadLine() loop that breaks upon receiving data

I have a program which relies on data being sent through a serial port. I would like to monitor when data is sent through with SerialPort.ReadLine(). My problem is that I use check boxes which freeze when checked because the SerialPort.ReadLine() method blocks until it receives some data. I have also tried using ReadTimeout() but it did not work; perhaps because I did not use it correctly.

I've posted my code for this event below. What I would like this method to do is to monitor my serial port when the checkbox is checked, and then stop monitoring the serial port when I un-check the box. My current situation with my code is that it freezes upon checking the box. All help is appreciated.

private void checkBox1_CheckedChanged(object sender, EventArgs e)
    {
        if (checkBox1.Checked)
        {
            checkBox1.Text = "Listening...";
            using (SerialPort arduino = new SerialPort())
            {
                arduino.BaudRate = 9600;
                arduino.PortName = comboBox1.Text;
                arduino.Open();

                string pipe = arduino.ReadLine(); //loop here

                if (pipe == "S")
                {
                    //System.Diagnostics.Process.Start("shutdown", "/f /r /t 0");
                    System.Windows.Forms.Application.Exit();
                }


                else
                {
                    checkBox1.Text = "Start";
                }
            }
        }
    }