Is there anything left to sanction in North Korea?

Foreign Policy Magazine posted an article on their website today entitled "Is there anything left to sanction in North Korea?"   I found this quote particularly interesting:

The 800-pound gorilla in the debate about the effectiveness of any sanctions is China. By the end of 2010, the last date for which there are records, China's trade with North Korea had boomed, surpassing $3.06 billion, up nearly 10 percent over 2008, according to figures cited by a U.N. panel monitoring enforcement of the North Korea sanctions.

At the conclusion of the article, George Lopez, a professor of peace studies at Notre Dame University, said that the sanctions would be more effective if China enforced them, and that the U.S. needs to convince China that they won't cause the downfall of the North Korean economy by enforcing the sanctions.  I thought this was a strange thing to say, since enforcing all the sanctions target the North Korean economy.