You could only use the <strong>
tag in the <a href>
.
I would change the following line
$title = '<a href="' . $title_pieces[0] . '" title="' . $title_pieces[1] . '">' . $title_pieces[1] . '</a>';
to
$title = '<a href="' . $title_pieces[0] . '" title="' . $title_pieces[1] . '"><strong>' . $title_pieces[1] . '</strong></a>';