How to convert string to utf-8 string in c#

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Text;

namespace adi.Web

{

    public partial class WebForm3 : System.Web.UI.Page

    {

        protected void Page_Load(object sender, EventArgs e)

        {

            System.Text.Encoding utf_8 = System.Text.Encoding.UTF8;

            string s = "adi";

            //string to utf

            byte[] utf = System.Text.Encoding.UTF8.GetBytes(s);

            //utf to string

            string s2 = System.Text.Encoding.UTF8.GetString(utf);

        }

    }

}