Fig. 6. Schematic illustration of SERS detection in the absence (A) and presence (C) of E. coli and (B and D) the corresponding Raman microscope image; (E) TEM image of E. coli without any treatment; (F) TEM image of SERS tags/E. coli/Fe₃O₄ sandwich structure; the Au@Ag-GO nanocomposites are indicated by arrows.