The Editor-in-Chief has retracted this article as the authors did not have permission to publish the data. Nguyen Sy Pham, Phuong Thi Que Phan and Bich Ngoc Nguyen agree to this retraction. Vinh Xuan Le has agreed to this retraction but not to the wording of this retraction note.

The online version of this article contains the full text of the retracted article as Supplementary Information.