<P>A green and facile fermentation method for the synthesis of carbon based dots (CDs) has been developed for the first time. The fluorescence (FL) properties of the obtained CDs could be tuned by changing the kind of microbes. For instance, the fermentation of leaves with <I>Bacillus subtilis</I> produces red emission CDs, which show great application potential in bioimaging. The formation mechanism and the FL mechanism of the CDs have been well discussed.</P><P>Graphic Abstract</P><P>A green and facile fermentation method for the synthesis of red-emission carbon based dots has been developed for the first time.<BR/><IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c8nj00705e'/><BR/></P>