Check for email exists or not using entity framework

Design Default.aspx page like bellow

Default.aspx.cs

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and write the bellow code in TextBox1_TextChanged in

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Gateway_TwoEntities gt = new Gateway_TwoEntities();
string email = TextBox1.Text;
var result = gt.tbl_param_requirement_cosultant_master.Where(v => v.email_address == email).Select(v => v.email_address).SingleOrDefault();
Label1.Text = result.ToString();
if (TextBox1.Text == Label1.Text)
{
Label2.Text = "* Email Already Exists";
}