The Editor-in-Chief and the publisher have retracted this article. This article was submitted to be part of a guest-edited issue. An investigation concluded that the editorial process of this guest-edited issue was compromised by a third party and that the peer review process has been manipulated. Based on the investigation's findings the Editor-in-Chief therefore no longer has confidence in the results and conclusions of this article.

Liang Zhang disagrees with this retraction. The Publisher has not been able to obtain a current email address for Jun Lu.

The online version of this article contains the full text of the retracted article as Supplementary Information.