Check Email Availability Using Ajax in codeigniter

<form id="reg_form">
<h5>Email Address</h5>
<input type="text" name="email" id="email" value="<?php echo set_value('email'); ?>" />
<div class="ajax_response_result"></div>
<input type="button" class="btn btn-primary" id="click_form" value="Submit" />
</div>
</form>

<script src="http://code.jquery.com/jquery-1.11.0.min.js"></script>
<script type="text/javascript">
$(document).ready(function() {
$(document).on('click','#click_form',function(){

jQuery.ajax({
type: "POST",
url: "<?php echo base_url('admin/emailcheck/ajax_signup') ?>",
data: $("#reg_form").serialize(),
success: function(res) {
$(".ajax_response_result").html(res);
}
});
});
});
</script>

<?php
class EmailCheck extends CI_Controller {

public function __construct()
{
parent::__construct();
$this->load->helper(array('form', 'url'));
$this->load->library('form_validation');
}

public function index()
{
$this->load->view('admin/signup_check');
}

public function ajax_signup()
{

$this->form_validation->set_rules('email', 'Email',
'required|is_unique[admin_info.email]');
$this->form_validation->set_message('is_unique', 'The %s is already taken');
if ($this->form_validation->run() == FALSE):
echo 'The email is already taken.';
else :
unset($_POST);
echo 'Available';
endif;
}

}

CREATE TABLE IF NOT EXISTS `admin_info` (
`id` int(11) NOT NULL,
`email` varchar(100) NOT NULL,
`username` varchar(250) NOT NULL,
`password` varchar(250) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;