[C#] How to save text from the multiline TextBox2 as Unicode Encoding?

Hello everyone.
This is my code for saveFileAs and saveFile for multiline TextBox2, and it works well.
When I save the text in TextBox2, to be saved as UTF-8 course. (example .txt, Encoding UTF-8).


But I want it to be saved as Unicode (UTF-16).
What needs to change or add in my code, that be text saved as Unicode (UTF-16), for example (.txt, Encoding Unicode)?
Please help me. Thank you.

Code:

private void saveToolStripMenuItem_Click(object sender, EventArgs e)
        {


            saveFileAs();
        }
        private void saveFileAs()
        {
            SaveFileDialog saveFileDialog1 = new SaveFileDialog();
            saveFileDialog1.Title = "Save file( .txt, .srt...)";
            saveFileDialog1.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
            saveFileDialog1.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*";
            saveFileDialog1.FilterIndex = 2;
            saveFileDialog1.RestoreDirectory = true;
            //Set default extension as .txt
            saveFileDialog1.DefaultExt = ".txt";




            if (saveFileDialog1.ShowDialog() == DialogResult.OK)
            {


                currentFile = saveFileDialog1.FileName;
                this.Text = currentFile + " File";
                saveFile();




            }
            toolStripButton8.Enabled = true;
            saveToolStripMenuItem.Enabled = true;
            toolStripButton12.Enabled = true;
            printToolStripMenuItem.Enabled = true;
            toolStripButton11.Enabled = true;
            printpreviewToolStripMenuItem.Enabled = true;
}
private void saveToolStripMenuItem_Click_1(object sender, EventArgs e)
        {
            saveFile();
        }
private void saveFile()
        {
            
            System.IO.StreamWriter sw = new System.IO.StreamWriter(currentFile);
            sw.Write(textBox2.Text);
            sw.Close();
            MessageBox.Show("saved!");


        }