在Ajax调用时，变量不被视为对象

I have a poll and when user click on one of the options, it sends data through ajax:

$.ajax({
    type: 'POST',
    url: '/poll.php',
    data: {option: option, IDpoll: IDpoll},
    dataType: 'json',
    async: false,
    error: function(xhr, status, error) {
          alert(xhr.responseText);
        },
    success: function(data) {
        if(data.msg == "0") {
            $( "#pollArea" ).load( "/pollVote.php", { allow: true }, function() {
                  alert( "Ďakujeme za Váš hlas!" );
                });
        }
        else {
            alert(data.msg);
            alert("V tejto ankete ste už hlasovali.");}
        }
    });

This works fine. Now data are passed to the file poll.php:

if (isset($_POST['option']) && isset($_POST['IDpoll'])) {
    require 'includes/config.inc.php';
    $ip     = $_SERVER['REMOTE_ADDR'];
    $option = $pdo->quote($_POST['option']);
    $IDpoll = $pdo->quote($_POST['IDpoll']);
    $date   = date("d.m.Y H:i:s");
    $poll   = new Poll();
    $msg    = $poll->votePoll($IDpoll, $ip, $option, $date);
    $arr    = array(
        'msg' => $msg

    );
echo json_encode($arr);

This also works, the problem happened in class Poll - method VotePoll:

public function votePoll($IDpoll, $ip, $option, $date)
    {
        try {
        $query  = "SELECT * FROM `votes` WHERE `IDpoll` = '$IDpoll' AND `ip` = '$ip'";
        $result = $this->pdo->query($query);    
        if ($result->rowCount() == 0) {
           /* do stuff */
      }
      catch (PDOException $e) {
        return $e->getMessage();
      }
    }

And the error message from the ajax call is following: Call to a member function rowCount() on a non-object. I know what this message means, but I can't find out why the variable $result isn't considered as PDO object. Strange thing is, that when I try to call function votePoll manually, it works perfectly and when I use var_dump on result it is PDO object. So where is the mistake?

EDIT: I forgot to say I was just editing this function. Originally it worked with mysqli but I wanted to switch to pdo (so query and stuff like that are okay).

So, this problem was in these lines:

   $option = $pdo->quote($_POST['option']);
   $IDpoll = $pdo->quote($_POST['IDpoll']);

PDO quote function add quotes to the string so option became 'option' etc. Then it was sent to query where additional quotes were added, so the result was ''option'' and that is error.