Simple error - CodeIgniter

[eluser]anna16[/eluser]
Hello guys

I have this codes below,

Code:

$query = $this->db->query('SELECT email_address FROM membership WHERE email_address="$this->input->post('email_address')"');

And this is the error message,

Code:

Parse error: syntax error, unexpected T_STRING

I hope someone can help me.

thanks.