Validation Script - Detecting Illegal Characters preg_match to find illegal characters

I'm trying to validate a user's desired username for a registration page. I want to detect any illegal characters being used for a username. So far i have managed to include most execpt the '\', the '\' is used for escape and treating the preceding characters literally. I try to do '\\' but i get an error because it execects another character.

$ck_result = "Default";$pattern = "/[!|@|#|$|%|^|&|*|(|)|_|\-|=|+|\||,|.|\/|;|:|\'|\"|\[|\]|\{|\}]/i";	// check for inputif($uname == '') {$ck_result = "<span class='error_header'>Required!</span>";}else if (preg_match($pattern, $uname)) {$ck_result = "<span class='error_header'>illegal characters</span>";}