return a mesage if no record found in ASP.Net

try
{
    string strConnString = ConfigurationManager.ConnectionStrings["ConnStr"].ConnectionString;
    SqlConnection con = new SqlConnection(strConnString);
    DataTable dt = new DataTable();

    using (SqlConnection conn = new SqlConnection(strConnString))
    {
        string strQuery = "SELECT * FROM TDLoanRate where LoanType Like'%" + txtValue.Text + "%'  ";
        SqlCommand cmd = new SqlCommand(strQuery);
        using (SqlDataAdapter sda = new SqlDataAdapter())
        {
            cmd.Connection = con;
            conn.Open();
            sda.SelectCommand = cmd;
            sda.Fill(dt);
            GridView1.DataSource = dt;
            GridView1.DataBind();
        }
    }
}

how do i check if there are no rows which has been searched and return a mesage