(A) SEM image showing E. coli bacteria embedded in NaCl crystals on the Si substrate with Cr-patterned fiducial grids. Cells appear as negative (dark) contrast regions in images. Scale bar is 20 μm. XRF images showing (B) Zn, (C) Ca, and (D) Cl distribution in the E. coli cells. (E) XRF image showing the co-localization of Zn, Ca and Cl in the E. coli cells. (F) Average XRF spectrum from the sample. Scale bar is 1 μm in (B–E).