我是否需要使用Doctrine查询来转义Symfony2上的字符串？

I've this code:
I get some data from a GET request:

$username = $request->get('username');

And then, I use doctrine to check if this username exists or not:

$found = $em->getRepository('Bundle:Users')->findByNick($username);
            if ($found){
               //nickname in use
            } else {
               //not found
            }

As you can see, I've no String escaping, so the value is directly sent to Doctrine. Is this a security issue? Should it be slashed for security reasons?
Note that I never use RAW queries, just prebuild ones from Doctrine.

There's no need to do it with prepared statements.

You can read here:http://docs.doctrine-project.org/projects/doctrine-dbal/en/latest/reference/security.html

And I've tried it out. This is the query generated by Doctrine:

WHERE t0.nick = 'dasdfaf\\' OR 1'

As you can see, several slashes were added.