You have to mention root as the second parameter of sendfile()
.
For example:
app.get('/:dir/:file', function(req, res) {
var dir = req.params.dir,
file = req.params.file;
res.sendfile(dir + '/' + file, {'root': '../'});
});
You can find more details here: https://github.com/visionmedia/express/issues/1465