The Editor-in-Chief has retracted this article. Following publication, concerns were raised regarding the ownership of the data. The corresponding author has stated that some of the data were obtained from a third party, and upon request has been unable to provide the raw data. The Editor-in-Chief therefore considers the article to be unreliable.

Jing Huang, Lijun Fu and Xiumei Wang agree to this retraction; Zhou Li, Dahe Lin, Chunhua Wang and Lifen Zhang, have not responded to any correspondence from the editor/publisher about this retraction.

The online version of this article contains the full text of the retracted article as Supplementary Information.