PHP PDO prepared statement -- MySQL LIKE query

I am trying to do a search through php's PDO class (mysql driver). I have the following query working with the MySQL client (table names changed to protect the innocent):

SELECT    hs.hs_pk, 
          hs.hs_text, 
          hs.hs_did, 
          hd.hd_did, 
          hd.hd_text, 
          hv.hv_text, 
          hc.hc_text 
FROM      hs 
LEFT JOIN hd 
 ON       hs.hs_did = hd.hd_did 
LEFT JOIN hd 
 ON       hd.hd_vid = hv.hv_id 
LEFT JOIN hc 
 ON       hd.hd_pclass = hc.hc_id
WHERE     hs.hs_text LIKE "%searchTerm%"
LIMIT 25;

This works like a charm regardless of the search term that I use. However, when I move to php, I can't get it to return anything. I have tried several different syntaxes that seem logical to work, but nothing I have tried works. here's my existing code:

$handle = fopen('/foo/bar/test.log', 'w+');
fwrite($handle, "doSearch, with search term: $searchTerm\n");
$sql = 
'SELECT   hs.hs_pk, 
          hs.hs_text, 
          hs.hs_did, 
          hd.hd_did, 
          hd.hd_text, 
          hv.hv_text, 
          hc.hc_text 
FROM      hs 
LEFT JOIN hd 
 ON       hs.hs_did = hd.hd_did 
LEFT JOIN hd 
 ON       hd.hd_vid = hv.hv_id 
LEFT JOIN hc 
 ON       hd.hd_pclass = hc.hc_id
WHERE     hs.hs_text LIKE :searchTerm
LIMIT 25';

try {
 $dbh = new PDO('mysql:host=localhost;dbname=awdb', "user", "password");
 fwrite($handle, "connected to DB\n");
 $prep = $dbh->prepare($sql);
 $ret = $prep->execute(array(':searchTerm' => '"%'.$searchTerm.'%"'));

 while ($row = $prep->fetch(PDO::FETCH_ASSOC)) {
  $i++;
  $result[$i]['subText'] = $row['hs_pk'];
  $result[$i]['subText'] = $row['hs_text'];
  $result[$i]['subDid'] = $row['hs_did'];
  $result[$i]['devDid'] = $row['hd_did'];
  $result[$i]['devText'] = $row['hd_text'];
  $result[$i]['vendorText'] = $row['hv_text'];
  $result[$i]['classText'] = $row['hc_text'];
 }
    $dbh = null;
}   
catch (PDOException $e) {
  print "Error!: " . $e->getMess