public static String ToCSV(this DataTable dt)
{
    StringBuilder sb = new StringBuilder();

    for (int x = 0; x < dt.Columns.Count; x++)
    {
        if (x != 0)
            sb.Append(",");
        sb.Append(dt.Columns[x].ColumnName);
    }
    sb.AppendLine();
    foreach (DataRow row in dt.Rows)
    {
        for (int x = 0; x < dt.Columns.Count; x++)
        {
            if (x != 0)
                sb.Append(",");
            sb.Append(row[dt.Columns[x]].ToString());
        }

        sb.AppendLine();
    }
    return sb.ToString();
}

<table>
	<thead>
		<tr><th>Header</th></tr>
	</thead>
	<tbody>
		<tr><td>Data</td></tr>
	</tbody>
</table>

public static void FixThead(this GridView grid)
{
    if (grid.Rows.Count > 0)
    {
        //This replaces <td> with <th> and adds the scope attribute
        grid.UseAccessibleHeader = true;
        grid.HeaderRow.TableSection = TableRowSection.TableHeader;
    }
}