XPath - 使用contains查找大括号

I need to find nodes which contain strings like that: {string} I would like to do it like that:

$nodeList = $xpath->query(".//*[text()[contains(.,'{" . $key . "}')]]", $dom);

I tried putting html, unicode etc codes there instead of curly brackets, also doubled the brackets, put slash (\) before them etc and it didn't work. How should it be accomplished?